For the past several months CUNA and NAFCU, through their own organizations and via the Electronic Payments Coalition, have been mounting an extensive advertising and lobbying campaign on the issue.

They also have worked with lobbyists for the two big banking trade associations in emphasizing the potentially negative impact on small financial institutions.

According to Roll Call, retail groups in Maine, Massachusetts, Minnesota and Rhode Island have backed bills in state legislatures to allow retailers to refuse to accept cards issued by smaller financial institutions, because the merchant would pay a smaller interchange fee.

Meanwhile, the National Retail Federation has run an extensive advertising and lobbying campaign to urge lawmakers not to delay the Fed rule, which was mandated by the Durbin Amendment in last year's financial overhaul bill.

John McKechnie, a former NCUA and CUNA official who now lobbies on financial issues, said credit unions' efforts have helped keep the issue alive.

"Credit unions are in the game; we now have a Senate floor opportunity on a bill that is likely to reach the president's desk,'' he said. "Now, we just have to win the damned vote."

The Fed issued a draft rule in December and was supposed to issue a final rule next month but has been delayed in doing so because it is still going through the large number of comments it received on the proposal. The final rule is supposed to take effect in July.

Acording to the proposed rule, the allowable costs for interchange would be limited to no more than the issuer's allowable costs divided by the number of electronic debit transactions on which the issuer received or charged an interchange transaction fee in the calendar year. Or the issuer could receive debit interchange capped at 12 cents per transaction.