Updated: 4:26 p.m.

Credit card and credit union representatives are crying foul after they were barred Thursday from a press conference Sen. Dick Durbin (D-Ill.) held on an interchange fee amendment he is sponsoring on the financial regulatory reform bill.

Members of the Electronic Payments Coalition say they were turned away from the Capitol after trying to attend the press conference.

“We were stopped at the front desk of the building — not even at the room — and turned away,” EPC spokeswoman Trish Wexler said. “I’ve never heard of such a thing. Turned away at the door of the room, sure. But Durbin’s staff is banning us from the whole building?”

Durbin spokesman Max Gleischman said that it was standard protocol to ban nonpress from press conferences in the Majority Whip’s office.

“Senator Durbin held a press conference in the conference room of his Capitol office,” Gleischman added. “Bank and credit card lobbyists came to the Capitol and asked to be let into our office without an invitation or an appointment. Our space is limited and we were barely able to accommodate all the reporters who wanted to attend, let alone lobbyists who are being paid to oppose this amendment. If the complaint here is that big bank and credit card lobbyists don’t have sufficient access to the U.S. Capitol, that doesn’t even meet the laugh test.”

The only nonpress invited to the event was the National Association of Convenience Stores President Henry Armour and a small Illinois grocer, who both spoke at the press conference, according to Gleischman.

“It’s the same reason not everybody can go to a press conference in the Radio/TV Gallery. They are not public parts of the Capitol,” said Gleischman, who noted that the event was standing-room only.

The skirmish over attending the event underscored the major lobbying battle under way over Durbin’s amendment, which is set to be debated Thursday. It would allow the Federal Reserve to regulate interchange fees, which banks and card companies charge merchants to process credit and debit transactions. Durbin’s amendment would also allow merchants to offer discounts to customers based on their payment method.

Interchange fees have never been voted on before on the floor of the Senate. But Durbin is leading the charge against big banks and major credit and debit card providers who have a lock on the business that Durbin refers to as “swipe fees.”

Community banks and credit unions are also opposing the amendment.

Durbin called out the Independent Community Bankers of America by name in the press conference, saying that the trade group isn’t representing its members because his amendment has an exemption for credit unions and community banks with assets of less than $10 billion. The ICBA “is one of the largest issuers of debit and credit cards,” Durbin said of the reason the trade association is opposing the bill.

Durbin also questioned the group’s name, wondering how it is “independent” if it votes with the larger banks. ICBA’s Steve Verdier said the group is planning on keeping its name.

Verdier also said his organization has done its own analysis of what the amendment would do and has “come to the conclusion that it is bad for community banks.”

The EPC’s Wexler said that every member company of her organization is putting out a massive call for grass-roots action.

Credit cards and banks aren’t alone in trying to stop the Durbin amendment. Several minority groups such as the Latino Coalition, the League of Rural Voters and the Minority Business Roundtable sent a letter Tuesday opposing the amendment.

“Community banks and credit unions consistently report that government intervention in the interchange system could drive them out of the payment-card business, threatening the survival of these pillars of community economic activity — the vast majority of which had nothing to do with the recent financial crisis — and reducing credit availability to small business owners and entrepreneurs,” the groups wrote.

The Merchants Payments Coalition, which supports the bill, has also ratcheted up its lobbying effort. Member companies, including the Food Marketing Institute, National Association of Convenience Stores, National Grocers Association, National Retail Federation, National Restaurant Association and the Retail Industry Leaders Association are listed on a print ad in Roll Call and Politico saying that credit card companies are “fleecing” consumers.

The one-week ad buy is in the mid-five-figure range, according to an MPC spokeswoman. MPC also has another similar-sized radio ad buy planned for the D.C. market this week.