The Federal Trade Commission is going after Amazon again, this time preparing a case that is its most ambitious attempt to reign in the e-commerce giant.

According to a report by Bloomberg, the FTC is preparing to sue Amazon for antitrust concerns regarding how it treats sellers using its platforms. The agency maintains that Amazon rewards sellers that fully buy into its platform and use its logistics services while punishing those that don’t.

The FTC already has already brought three cases against Amazon, but this one could be the most high-stakes yet, with Bloomberg indicating Chair Lina Khan may pursue structural changes to Amazon.

This isn’t the first time Amazon has been in trouble for its dealings with third-party resellers. In late 2022, Amazon reached an agreement with the EU to end investigations stemming from the company’s practices. Amazon was accused of using third-party seller data to improve its own retail offerings and gain an unfair advantage. The EU similarly accused the company of unfairly rewarding sellers that used its logistics services with “Buy Box” placement.

As Bloomberg points out, Khan has signaled in the past that, unlike the EU, she is not open to compromise agreements, telling a Senate subcommittee that she would “strongly disfavor” such an outcome. Given that the EU’s compromise with Amazon only led to changes in the EU, and not worldwide, it’s hard to argue with the belief that such compromises have limited effect, especially when considering that even the EU’s agreement expires after seven years.

Should the FTC move forward with the case, it could ultimately prove as big or bigger than the US antitrust case against Microsoft in 2001.