UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

(Rule 14a-101)

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No.    )

Filed by the Registrant  ☒                            

Filed by a Party other than the Registrant  ☐

Check the appropriate box:

Aegion Corporation

(Name of Registrant as Specified in Its Charter)

(Name of Person(s) Filing Proxy Statement if other than Registrant)

Payment of Filing Fee (Check the appropriate box):

Client Letter

[Dear NAME / INSERT GREETING],

I’m reaching out to share an important development for Aegion. We have announced an agreement under which affiliates of New Mountain Capital will acquire our company. Upon completion of the transaction, Aegion will become a private company and no longer be listed on the NASDAQ stock exchange. The press release we issued is attached.

This transaction represents an exciting new chapter for Aegion, and we are confident that it will enable us to better serve clients like you for years to come. New Mountain supports our strategy and, as a private company, we will have the resources and long-term approach to advance our technology investments and new product offerings. Moreover, New Mountain brings deep industry knowledge, strong operational expertise and a proven track record of supporting businesses through investments in R&D and capital expenditures that recognize the value of achieving differentiated long-term growth – which we will leverage to deliver new and transformational solutions to you.

For clients of Aegion Energy Services, as you know, we recently announced a process to divest this business segment. Upon the close of the transaction, New Mountain will review the previously announced sales process for Aegion’s Energy Services segment and determine what best positions the business for long-term success. Aegion Energy Services will continue to serve clients as always.

In terms of next steps, the transaction is expected to close in the second quarter of 2021, at which time we expect to operate largely how we do today in the many communities where we work. Further, New Mountain is committed to maintaining our significant presence at our field offices around the world. Upon completion of the transaction, we will retain the Aegion name, our same business unit subsidiaries and brands and become a portfolio company of New Mountain Capital. We expect the transition to be seamless for you, and we do not expect the transaction to have any impact on our contracts or how we do business with you today. Simply put, it is business as usual, and we remain focused on delivering safe and exceptional performance.

On behalf of the Aegion team, thank you for your continued support. Maintaining our focus on our clients remains our top priority, and we look forward to continuing our partnership.

If you have any questions, please contact [me / your usual Aegion contact].

Sincerely,

NAME

Forward-Looking Statements

This communication contains “forward-looking statements” within the meaning of the U.S. federal securities laws. Such statements include statements concerning anticipated future events and expectations that are not historical facts. All statements other than statements of historical fact are statements that could be deemed forward-looking statements. Forward-looking statements are typically identified by words such as “believe,” “expect,” “anticipate,” “intend,” “target,” “estimate,” “continue,” “positions,” “plan,” “predict,” “project,” “forecast,” “guidance,” “goal,” “objective,” “prospects,” “possible” or “potential,” by future conditional verbs such as “assume,” “will,” “would,” “should,” “could” or “may,” or by variations of such words or by similar expressions or the negative thereof. Actual results may vary materially from those expressed or implied by forward-looking statements based on a number of factors, including, without limitation: (1) risks related to the consummation of the merger, including the risks that (a) the merger may not be consummated within the anticipated time period, or at all, (b) the parties may fail to obtain stockholder approval of the merger agreement, (c) the parties may fail to secure the termination or expiration of any waiting period applicable under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, (d) other conditions to the consummation of the merger under the merger agreement may not be satisfied, and

(e) the significant limitations on remedies contained in the merger agreement may limit or entirely prevent the Company from specifically enforcing the obligations of Carter Intermediate, Inc. (Parent) and its wholly owned subsidiary, Carter Acquisition, Inc. (Merger Sub), under the merger agreement or recovering damages for any breach by Parent or Merger Sub; (2) the effects that any termination of the merger agreement may have on the Company or its business, including the risks that (a) the Company’s stock price may decline significantly if the merger is not completed, (b) the merger agreement may be terminated in circumstances requiring the Company to pay Parent a termination fee, or (c) the circumstances of the termination, including the possible imposition of a 12-month tail period during which the termination fee could be payable upon certain subsequent transactions, may have a chilling effect on alternatives to the merger; (3) the effects that the announcement or pendency of the merger may have on the Company and its business, including the risks that as a result (a) the Company’s business, operating results or stock price may suffer, (b) the Company’s current plans and operations may be disrupted, (c) the Company’s ability to retain or recruit key employees may be adversely affected, (d) the Company’s business relationships (including, customers, franchisees and suppliers) may be adversely affected, or (e) the Company’s management’s or employees’ attention may be diverted from other important matters; (4) the effect of limitations that the merger agreement places on the Company’s ability to operate its business, return capital to stockholders or engage in alternative transactions; (5) the nature, cost and outcome of pending and future litigation and other legal proceedings, including any such proceedings related to the merger and instituted against the Company and others; (6) the risk that the merger and related transactions may involve unexpected costs, liabilities or delays; (7) other economic, business, competitive, legal, regulatory, and/or tax factors; and (8) other factors described under the heading “Risk Factors” in Part I, Item 1A of the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2019, as updated or supplemented by subsequent reports that the Company has filed or files with the SEC. Potential investors, stockholders and other readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date on which they are made. Neither Parent nor the Company assumes any obligation to publicly update any forward-looking statement after it is made, whether as a result of new information, future events or otherwise, except as required by law.

Additional Information and Where to Find It

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval. This communication may be deemed to be solicitation material in respect of the proposed merger between Merger Sub and the Company. In connection with the proposed transaction, the Company plans to file a proxy statement with the SEC. STOCKHOLDERS OF THE COMPANY ARE URGED TO READ THE PROXY STATEMENT (INCLUDING ANY AMENDMENTS OR SUPPLEMENTS THERETO AND ANY DOCUMENTS INCORPORATED BY REFERENCE THEREIN) AND OTHER RELEVANT DOCUMENTS IN CONNECTION WITH THE PROPOSED TRANSACTION THAT THE COMPANY WILL FILE WITH THE SEC WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION AND THE PARTIES TO THE PROPOSED TRANSACTION. Stockholders and investors will be able to obtain free copies of the proxy statement and other relevant materials (when they become available) and other documents filed by the Company at the SEC’s website at www.sec.gov. Copies of the proxy statement (when they become available) and the filings that will be incorporated by reference therein may also be obtained, without charge, by contacting the Company’s Investor Relations at kcason@aegion.com or 1.800.325.1159.

Participants in Solicitation

The Company and its directors, executive officers and certain employees, may be deemed, under SEC rules, to be participants in the solicitation of proxies in respect of the proposed transaction. Information regarding the Company’s directors and executive officers is available in its proxy statement filed with the SEC on March 6, 2020. Other information regarding the participants in the proxy solicitation and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the proxy statement and other relevant materials to be filed with the SEC (when they become available). These documents can be obtained free of charge from the sources indicated above.