BY JANESS ANN J. ELLAO Bulatlat Posted 6:00 p.m., May 12, 2008 The Pagkakaisa ng mga Samahan ng Tsuper at Operator Nationwide (Piston) spearheaded a nationwide transport strike today to demand the repeal of the Oil Deregulation Law and the cancellation of the 12-percent value-added tax (VAT) on oil amid continuing oil price hikes. Piston…