The Office of Fair Trading (OFT) has said it is examining the Wood Group's £600m takeover of its rival PSN.
The OFT said it was considering whether the deal would result in a "substantial lessening of competition within any market or markets".
The OFT could demand action from the companies or refer the acquisition to the Competition Commission for further investigation.
Wood said its takeover of PSN would create a "global leader" in its field.
PSN is an international energy services company employing more than 8,000 people worldwide and operating in 23 countries.