Sen. Elizabeth Warren (D-Mass.) is drafting a bill that would call on regulators to retroactively review about two decades of “mega mergers” and ban such deals going forward.

Warren’s staff recently circulated a proposal for sweeping anti-monopoly legislation, which would deliver on a presidential campaign promise to check the power of Big Tech and other industries. Although the Trump administration is currently exploring their own antitrust probes, the proposal is likely to face resistance from lawmakers.