The CH2M board of directors has written to its shareholders urging them to vote in favour of the £2.15bn merger proposal with rival US consultant Jacobs.
The merger is still awaiting the results of a review from the regulatory agencies, but if approved there will be a special shareholders meeting where merger proposals will be discussed.
Documents from Jacobs said boards from both companies had unanimously approved the merger.
Last week, Jacobs filed a preliminary S-4 registration document with regulatory body the Securities and Exchange Commission (SEC) for review. The document provides SEC with the essential facts for the merger allowing the body to guard against fraud.
CH2M said it had approached Jacobs with a merger proposal as it had wanted to effect change having outgrown its employee ownership structure as a global business with $5.4bn (£4bn) in revenue.
In the deal, Jacobs will acquire all of the CH2M’s outstanding shares in a 60% cash and 40% stock transaction with CH2M shareholders receiving one of three options for payment of each share.
The mega merger, which will see Jacobs grow by an estimated 20,000 to 74,000 staff, will make Jacobs one of the world’s largest engineering consultants.