Every once in a while, when you least expect it, Congress manages to throw a bone to the little guys!

WASHINGTON — Retailers have begged Congress for years, in vain, to limit the fees they must pay to banks when customers swipe credit or debit cards. Bills never reached a vote. Amendments were left on the table. The Senate did not even grant the courtesy of a committee hearing.

That long record of futility ended in a landslide Thursday night. Sixty-four senators, including 17 Republicans, agreed to impose price controls on debit transactions over the furious objections of the beleaguered banking industry.

The amendment to the Senate’s sweeping financial legislation could save billions of dollars for family restaurants and dry cleaners, Wal-Mart and Amazon.com, and every other business whose customers increasingly pay with debit cards. It does not address credit card fees directly.

Consumers also could save money, particularly at businesses like grocery stores that compete on price. But some experts warned that lower profit margins could lead banks to curtail bank card reward programs.

The Senate approved a series of amendments unfavorable to the banking industry over the last week, but this one was widely regarded as the most surprising. Meddling in dealings between businesses generally is anathema to Republicans and a relatively low priority for Democrats.

And this was not an easy vote. Lobbyists for the wounded but formidable banking industry made clear to some senators that this decision would affect future campaign donations, according to people who participated in those conversations.

But retailers mounted an unusually effective yearlong campaign to frame the issue as a chance for Congress to help small business. A leading trade group for chain retailers worked with small-business groups to make sure that every time a senator held a town hall meeting back home, a local business owner showed up to ask about card fees.