UPDATE 1-U.S. refinery strike widening to include largest refinery
(Adds additional strike notices, USW statement) HOUSTON, Feb 20 (Reuters) - The U.S. refinery strike was widening on Friday night as workers at the nation's largest refinery gave notice of a walkout beginning at 12 a.m. (0600 GMT) on Saturday, the United Steelworkers union (USW) said.