This is tremendous. As the largest employer in the country, their agreement will make a real difference to the congressional fight over healthcare reform. Again, an incremental step in the process, but it's a good sign:

WASHINGTON — Wal-Mart, the nation’s largest private employer, joined hands with a major labor union Tuesday to endorse the idea of requiring large companies to provide health insurance to their workers, a move that gives a boost to President Obama as he is pushing for health legislation on Capitol Hill.

“Not every business can make the same contribution, but everyone must make some contribution,” Wal-Mart’s chief executive, Michael T. Duke, wrote in a letter to White House and Congressional officials, adding that he favored “an employer mandate which is fair and broad in its coverage.”

The letter was issued jointly with Andrew W. Stern, president of the Service Employees International Union, which represents two million workers, many of them in the health care industry, and John D. Podesta, who ran Mr. Obama’s transition to the presidency and leads the Center for American Progress, a Democratic policy organization here.

But Wal-Mart’s embrace of the employer mandate may come at a price. In its letter, the company says that if Congress imposes a requirement that employers offer insurance, it must also offer a guarantee to business that health care costs will in fact be contained, perhaps through a so-called trigger mechanism that would impose reductions if certain spending targets were not met.

“We’re for an employer mandate, but we believe that it has to be accompanied by these measures that are really going to deliver on the savings,” said Leslie A. Dach, Wal-Mart’s top lobbyist, who met with Rahm Emanuel, the White House chief of staff, on Tuesday afternoon to discuss the proposal. “If any business is going to be asked to take on an employer mandate, to face changes in the tax laws, there should be some sense that the promise of the bill to reduce health costs will actually occur.”

The employer mandate is central to Mr. Obama’s plan for expanding health coverage to the nation’s 46 million uninsured, but many companies, including Wal-Mart, have long resisted the idea. But as health legislation moves through Congress, representatives of industry are becoming increasingly convinced that they must join forces with the administration to have a seat at the negotiating table.

The trade group representing pharmaceutical companies recently promised to cut the cost of prescription drugs by $80 billion over 10 years, and Democratic officials said hospitals were close to reaching a similar agreement on cost-cutting with the Obama administration. Mr. Emanuel said Tuesday afternoon that chief executives of other companies — he did not specify which — had also expressed interest in embracing an employer mandate.

“Everybody is now trying to get their seat on the train,” Mr. Emanuel said.