King Soopers employees in metro Denver and Boulder will vote Jan. 29 and 30 on authorizing a strike against the supermarket chain. About 10,000 members of United Food and Commercial Workers Local 7 will be eligible to vote. The employees’ contract with King Soopers expired Friday, Jan. 17 after the company made what it called its “last, best and final offer.” Contracts at other Colorado King Soopers and City Market stores, all owned by Kroger, expire in February.