New York Attorney General Letitia James is investigating whether Capital One's (COF.N) proposed $35.3 billion takeover of Discover Financial Services (DFS.N) violates the state's antitrust law.
In court filings on Wednesday, James asked a state judge in Manhattan to subpoena Capital One for documents needed for her probe, citing the bank's alleged lack of cooperation.
James said a merger could have a significant impact in New York because Capital One and Discover respectively have more than $9.5 billion and $6.5 billion of credit card loans there.
She also said the impact of a merger would be "particularly felt by the often vulnerable New Yorkers with subprime credit scores."
Neither company immediately responded to requests for comment.
Capital One, based in McLean, Virginia, is one of the largest U.S. banks, with $480 billion of assets as of June 30. It expects to report third-quarter results on Thursday.
Discover, based in Riverwoods, Illinois, reported a $965 million third-quarter profit last week.
Announced in February, the all-stock merger would create the largest U.S. credit card issuer with more than $250 billion of outstanding loans, surpassing JPMorgan Chase (JPM.N), and access to more than 305 million cardholders.
James said the merger would extend Capital One's lead as the largest U.S. subprime card issuer, and give the combined company a more than 30% market share.
A merger would also help Capital One, which issues Visa- and Mastercard-branded cards, expand its payment operations.
The merger requires approvals by shareholders, various bank regulators, the Department of Justice and Federal Trade Commission. Capital One and Discover have said they hope to close the deal by early 2025.
James said her office asked Capital One and Discover in May to waive confidentiality so it could review documents they submitted to the Justice Department's antitrust division.
Discover agreed to a full waiver but Capital One did not, claiming it would give New York unlawful "visitorial power" over national banks, leading to the subpoena, James said.
Some customers sued Capital One and Discover in July over the merger, saying it would reduce competition and boost consumer costs.
