Wal-Mart Stores Inc , the world's largest retailer, said on Tuesday that it supports President Barack Obama's push to require large employers to offer health insurance to workers.

We are for an employer mandate which is fair and broad in its coverage, stated a letter addressed to Obama and signed by Mike Duke, the chief executive of Wal-Mart; Andy Stern, the president of Service Employees International Union (SEIU) and John Podesta, the CEO of the Center for American Progress.

Wal-Mart's public statement of support for employer mandated coverage comes as Obama pushes for an overhaul of the $2.5 trillion U.S. healthcare system. He has made a healthcare plan that reins in costs and covers most of the roughly 46 million uninsured Americans one of his top priorities.

While the president has left much of the details of health reform to Congress, he has told U.S. lawmakers he is open to requiring larger companies to provide coverage for employees but exempting smaller businesses.

In recent years, Wal-Mart, the nation's largest private employer, has come under fire by labor-backed critic groups that accused it of mistreating employees and not offering adequate healthcare coverage.

Wal-Mart has worked to counter critics by promoting its healthcare initiatives, such as its $4 generic drug program. In 2007, it also joined with the SEIU, which has more than 1 million members, in calling for universal health-care coverage for all Americans by 2012.

Wal-Mart said it supports an employer mandate that covers as many businesses as possible, as well as part-time and full-time employees. The requirement would ultimately save companies money, it added.

This choice will require employers to consider the trade-off of agreeing to a coverage mandate and additional taxes versus the promise of reduced health care cost increases, it said.

It also said health care reform legislation should include provisions that reduce health costs, and that the retailer would support legislation that would put a public healthcare plan in place should private health insurers fail to meet price and competition targets, also known as a trigger provision.

(Reporting by Nicole Maestri; Additional reporting by Susan Heavey in Adelphi, Maryland; Editing by Tim Dobbyn and Richard Chang)