Once Joe Biden was elected president, companies contemplating mergers knew the U.S. government would take a harder line on deal making. Still, they figured it would take regulators a little time to find their groove amid the many layers of bureaucracy in Washington.

Lina Khan had a different idea. Since she took over the Federal Trade Commission—one of the two major agencies tasked with U.S. federal antitrust enforcement—in mid-June, she has used a variety of procedural gambits to slow down merger reviews. The agency has rescinded a ’90s-era policy that made it easier for companies to settle merger cases, and told companies it would issue formal warning letters about the legal risks they will face if they consummate deals the FTC has been too busy to review.

That policy could spook companies and their shareholders. At least one tech acquisition that was expected to easily pass FTC muster, involving the online real estate site Zillow, is stuck on Khan’s desk.