The United Steelworkers accused US Steel of "petty" negotiating tactics as discussions entered a critical stretch, saying they have made little progress on key issues. In a text message to union members on Sunday, the Steelworkers bargaining committee said the discussions have yet to yield concessions from the steel producer, which is owned by Nippon Steel Corp., on healthcare, job protection and other issues. The union's frustration grows as the deadline approaches with no breakthrough in sight.