House Democrats are putting their mouths where their bank fees are: a group sent a letter to U.S. Attorney General Eric Holder demanding an investigation into the fee hikes several major banks have announced recently.

The liberal leaders suspected that the new fees might violate federal antitrust laws.

The change that has caused the most public outcry is Bank of America's decision to charge debit card users a $5 monthly fee.

Lawmakers who signed the letter (PDF) said that they were suspicious that banks were communicating and colluding to assign fees that were unfair to consumers.

"There is clearly no problem with banks making independent business decisions based upon the landscape as they see it," the letter reads in part. "Antitrust issues are raised, however, if they are attempting to facilitate group decisions on their prices, terms and conditions."

The members of Congress also cited several instances of bank executives warning that consumers would pay the price for Congress' actions regulating overdraft fees and per-transaction fees for purchases made with debit and credit cards.

One such statement, recorded in May, is from Independent Community Bankers Association President Jerry C. Walker.

"Free checking is going to be gone," he said. "You can kiss that away. If you want a debit card, there are going to be (extra) fees."

The Dodd-Frank Wall Street Reform and Consumer Protection Act passed by Congress earlier this year restricted banks' ability to assess fees to their customers.

Rep. Raul M. Grijalva (D-AZ), co-chair of the Congressional Progressive Caucus, co-signed the letter with Reps. Peter Welch (D-VT), CPC co-chair Keith Ellison (D-MN), John Conyers (D-MI) and Mike Honda (D-CA).

"Americans aren’t money trees to be held upside down and shaken until there’s nothing left," Grijalva said in a prepared statement. "We instituted the Dodd-Frank banking law last year because banks are running rampant and squeezing families out of every penny. Now that those rules are going into effect, big bankers are trying to find new and potentially illegal ways to keep squeezing. We need a fair market for banking services in this country, and if the big banks work together to raise fees at the same time, that’s the opposite of choice and competition."

AFP photo.