A minimum-wage ballot initiative covering employees of most businesses operating at Denver International Airport has been cleared for the May 7 municipal election. The Denver Elections Division certified Monday that the union-backed Denver Airport Minimum Wage Initiative met the petition signature threshold. If approved by voters in the spring, the initiative would require most contractors and other employers with more than 30 employees at DIA to pay a minimum wage of $13 an hour, ratcheting up to $15 by mid-2021.