The CLEAN Mergers Act is designed to give the government stronger tools to challenge and unwind large corporate mergers that may have been approved improperly or without adequate scrutiny. The bill focuses on two main categories of deals: massive mergers worth $10 billion or more (called "threshold transactions"), and any other mergers completed between January 2025 and January 2029 that the government believes were approved with problems (called "enforcement-lapse transactions").

For the biggest deals ($10 billion+), companies have 180 days after the law passes to either sell off the merged assets or keep them completely separate while the government reviews the deal. Companies can ask a court to let them keep the merger if they can prove it didn't significantly reduce competition—for example, by showing the combined company doesn't control too much market share or that prices and quality haven't suffered.

For other mergers completed during this four-year period, the government gets two years to investigate whether something went wrong during the approval process. This includes checking for things like fraud, violations of law, political pressure on regulators, conflicts of interest, or foreign government interference. If the government finds problems, it can order the companies to break up the deal. Companies can challenge this in court, but they have to prove by clear and convincing evidence that the problems didn't actually happen or were so minor they shouldn't matter.

The law also makes it easier for the government to pursue these cases by extending the time limit for antitrust lawsuits from four years to ten years, and it requires companies to preserve all communications and documents related to their mergers. If companies destroy evidence, courts can assume the missing evidence would have hurt their case. Companies that refuse to divest when ordered face daily fines up to $100,000 or 5% of the deal's value, and courts can appoint a trustee to force the sale of assets.