A flurry of antitrust enforcement actions in the last month has corporations suddenly paying more heed to whether their merger deals will pass muster with federal regulators.

Since early December, the Federal Trade Commission and the Justice Department have filed complaints three times to undo completed acquisitions—even though the deals were exempt from notification requirements of the Hart-Scott-Rodino Act. That alone should make corporate counsels and compliance departments take notice, experts say.

Jaclyn Jaeger is a freelance contributor to Compliance Week after working for the company for 15 years. She writes on a wide variety of topics, including ethics and compliance, risk management, legal,...