Postal workers held rallies across the country on Tuesday to back legislation that would repeal a benefit-funding mandate they say lies behind the Postal Service’s financial woes. A 2006 law has forced the USPS to become the only agency required to fund 75 years of retiree health benefits over just a 10-year span. The American Postal Workers Union says the requirement accounts for 100 percent of the service’s $20 billion in losses over the previous four years, without which the service would have turned a profit. A Democratic-backed measure before Congress would undo the mandate. Republicans meanwhile are trying to push a bill that would establish an unelected board to overhaul the USPS and likely force mass layoffs. The postal workers’ union says protests were organized Tuesday in every congressional district.