Wal-Mart, the nation’s largest private employer, sent a letter to President Obama and congressional officials expressing support for an employer mandate that would require large companies to provide health insurance to their workers. As reported by Kaiser Health News and the Associated Press, Wal-Mart’s chief executive, Michael Duke, was joined in signing the letter by Andrew L. Stern, president of the Service Employees International Union, which represents more than a million healthcare workers, and John Podesta, who leads the Center for American Progress. The letter also states that any employer mandate should be balanced by a healthcare cost containment guarantee, perhaps through a trigger mechanism that would impose reductions if designated spending targets were not met.