FORTUNE – It took a 14,999,999% pay increase to finally put the “say on pay” regulations in the Dodd-Frank bank reform to the test on Wall Street.

Shareholders at Citigroup (C) on Tuesday voted against giving CEO Vikram Pandit a $15 million raise for 2011. He had made $1 the year before. It’s the first time shareholders have rejected the executive pay packages of a major bank since Dodd-Frank made the votes mandatory a year ago. The vote came at Citigroup’s annual shareholder meeting, which is being held in Dallas. The question is what happens next?

While Dodd-Frank mandates shareholders at all companies, not just banks, get a vote on executive compensation each year, companies don’t have to comply with those votes. It’s not clear what Citi will do. Effectively 55% of Citi’s shareholders voted to reject the pay packages of Pandit and Citi’s other executives. The company released a statement that said the company’s board of directors will take the vote “seriously,” and try to understand shareholder concerns. “The Personnel and Compensation Committee of the board will carefully consider their input as we move forward,” said the statement.

Charles Elson, director of the John L. Weinberg Center for Corporate Governance, says in other industries so-called “say on pay” votes have been effective at reducing executive pay packages. Wall Street, though, has been historically unresponsive to critics that say bank pay is too high. Recently, a number of investment banks have switched to paying their employees more in stock, rather than huge year-end cash bonuses.

Elson says there were more than two dozen votes last year in which shareholders objected to a company’s executive pay. Nearly all of them resulted in the companies cutting their pay packages. General Electric adjusted its executive pay after shareholders objected last year. In other instances, shareholders have sued, though many of those suits have so far not been successful. “Citi would be foolish to ignore the vote,” says Elson. “Though I think is more about a broader shareholder dissatisfaction with how the company is being run.”

The shareholder vote at Citi has to do with what Pandit received in 2011. The CEO was awarded a pay package of $14.9 million. Pandit has already been paid nearly $7 million in cash for his work last year. The rest of his pay was made in restricted stock and cash, which was expected to be paid to Pandit over the next few years. It is likely that this is the portion of Pandit’s pay that Citigroup could restructure. Pandit’s pay package for 2011 does seem excessive. It topped the pay of a number of other Wall Street CEOs, including Goldman’s Lloyd Blankfein. What’s more, since the end of 2006, Citigroup’s market cap has plunged $180 billion or 64%. By that measure, and past CEO compensation, Pandit should be making roughly $9 million, not $15 million.

The Citi vote may signal a new wave of disapproval of Wall Street and CEO pay. Citigroup is the first of the major banks to hold what could be a somewhat contentious season of annual meetings between shareholders and company management for financial firms. Shares of the major banks fell dramatically last year. Nonetheless, most banks approved eight-figure pay packages for their CEOs.