Aggressive antitrust scrutiny of planned megamergers has led to jaw-dropping payouts from buyers to their targets in recent months. It’s also deterring some deals between market competitors that might otherwise have been struck, according to leading antitrust lawyers.

On Tuesday, a federal judge in Washington, D.C. upheld a Federal Trade Commission injunction blocking the proposed $6.3 billion merger of the two leading office supply chains, Staples Inc. and Office Depot Inc. Just last week, the No. 2 and No. 3 largest oil fields services companies, Halliburton Inc. and Baker Hughes Inc., scrapped their $34.6 billion merger plan after an unsuccessful 17-month effort to overcome U.S. and European antitrust hurdles.