Wal-Mart, the biggest private employer in US, sided with a major labor union on Tuesday to back the proposal of large companies providing health insurance to their employees.

In a letter to the White House and officials of the Congress, Wal-Mart chief executive Michael T.Duke emphasized the need for every business to make some contribution to employees’ welfare programs. The letter was issued jointly with the president of Service Employees International Union, Andrew W.Stern as well as John D.Podesta who heads the Center for American Progress.

The endorsement by Wal-Mart of the idea of employer mandate in employees’ health programs comes as a welcome move for US President Obama who is poised to push his health legislation in the Capitol Hill. The employer mandate is crucial to the President’s health coverage plan which if passed will extend medical insurance to around 48 million uninsured people in the country. However Mr. Obama’s proposals have long met with resistance from private businesses which have traditionally opposed any form of employer mandate in health insurance programs.

However Wal-Mart’s support for employer mandate may come with riders. The company has made it clear in its letter that if the Congress makes it mandatory for private employers to offer health insurance, it must also ensure that health costs will be kept within limits.