Service Employees International Union, one of the state’s largest and most politically active unions, has begun gathering signatures on an initiative that would repeal the state sales tax exemption for out-of-state residents. The campaign’s launch comes just days after the House of Representatives abandoned an attempt to do away with the tax break.A lone initiative petition signature-gatherer was spotted Friday at a Walmart store in Lacey, according to the Washington State Wire, an Olympia-based business news service.Adam Glickman, vice president of SEIU Healthcare 775NW, which represents all of the state’s 40,000 home health care workers, said the union was “just testing the water” and had made no decision on whether to launch a full-scale effort to put the measure on the November ballot.According to Washington Public Disclosure Commission filings, the union has transferred $500,000 into an account dedicated to passing the measure, Initiative 1167. Glickman said in an email that ending the exemption, which is popular among Vancouver retail businesses, would yield an estimated $66 million per biennium to fund training programs for home-care workers. The initiative would eliminate the tax break for residents of Alaska, Oregon, Montana and the Canadian province of Alberta on purchases made in Washington. It would also impose the sales tax on bill collectors.