Thousands of Verizon Communications Inc workers on the U.S. East Coast could strike on Sunday with no sign of an agreement as contract negotiations with unions went to the wire, a union spokeswoman said on Saturday. The largest U.S. wireless service provider has been locked in negotiations centering on healthcare costs and other issues, ahead of Saturday's expiry of contracts covering almost 40,000 wireline service workers in nine eastern states and Washington, D.C. Candice Johnson, a spokeswoman for the Communications Workers of America , said the workers could go on strike on Sunday.