Visa Inc’s $5.3 billion acquisition of fintech startup Plaid Inc is facing antitrust scrutiny following the U.S. Justice Department filing a court petition on Tuesday demanding more information on the transaction.

The DoJ is reviewing the proposed deal to check whether it violates provisions of antitrust law. It has filed a petition with a U.S. district court in Massachusetts, asking it to require consulting firm Bain & Co to turn over documents wanted as part of the antitrust review, including some that discuss Visa’s strategies around pricing and competition with other debit card networks.

In a statement the DoJ said, Bain was “asserting unsupported claims of privilege over the documents.”

Bain did not immediately respond to requests for comments.

Neither the Justice Department nor Visa immediately responded to requests for comments.

Plaid declined to comment.