The expanded merger-review process the Federal Trade Commission proposed this week would require companies to file detailed information at the outset on how deals affect labor markets, a new requirement that’s fueling concern among businesses that regulators now will seize on plans for steep job cuts as a justification for blocking transactions that previously sailed through.

Companies often help win investor support for mergers by highlighting “synergies” in the form of sweeping layoffs made possible by combining overlapping operations. But the FTC’s move suggests that selling point might become a major liability in winning regulatory approval, some antitrust and regulatory attorneys say.