WASHINGTON – Democratic lawmakers are asking the Justice Department to investigate whether Bank of America and other major banks improperly worked together to charge customers new monthly fees for using their debit cards.

Rep. Peter Welch, D-Vt., and four other Democrats said Thursday that they’ve asked Attorney General Eric Holder to see if big banks violated antitrust laws before announcing the fees.

Welch said the lawmakers have no evidence of collusion. But he said the timing of the fees merits an investigation.

“You don’t have a competitive marketplace,” Welch said at a news conference.

Bank of America said last month that it would charge its customers $5 a month if they use their debit cards for purchases. Customers who use their cards only at ATMs will not have to pay the fee.

Chase and Wells Fargo are also testing $3 monthly debit-card fees in select markets.

SunTrust, a regional bank based in Atlanta, began charging a $5 debit card fee in June for customers with basic checking accounts.