Aberdeen offshore company Subsea7 is set to sell part of the joint business being created through its takeover by London-based Acergy.
The Office of Fair Trading (OFT) has said the two oil field services firms should offload a portion of their specialist pipe-laying business.
They are two out of the three competitors in the market.
The OFT is requiring the newly-merged company to get permission for its choice of buyer.
Acergy announced the acquisition of Subsea7 in June, creating a company with 12,000 employees and with a joint market value of billions of pounds.