The Consumer Financial Protection Bureau is preparing to sue Santander Bank, alleging that the Spanish bank overcharged borrowers on auto loans, two sources familiar with the plans said on Friday.

The action by the CFPB could come as early as today, said the sources, who requested anonymity because they were not authorized to speak about the matter.

Santander spokeswoman Raschelle Burton on Friday declined to comment. A spokesman for the CFPB did not immediately respond to a request for comment. According to the sources, the lawsuit centers on a financial product known as “guaranteed auto protection” (GAP) that can shield a car buyer from some of the expense of a serious collision.

If a driver’s auto insurance only covers replacement cost, GAP coverage may cover the entire balance of the loan.

Consumers often purchase GAP insurance in the dealer showroom and the costs are built into the car loan.

Federal and state officials have been looking into whether consumers have been paying for unneeded GAP insurance or have seen their loan rates climb too high when GAP coverage was added.

Reuters reported last month that the Office of the Comptroller of the Currency was examining how Wells Fargo administered its auto loan business.

Santander Consumer USA Holdings Inc. agreed to pay at least $9.35 million to resolve charges that it improperly repossessed cars of members of the U.S. military in 2015. It neither admitted nor denied any wrongdoing.

Santander Consumer USA Holdings agreed in March to pay $22 million in connection with what Massachusetts Attorney General Maura Healey called a first-in-the-nation settlement involving subprime auto loan securitization.