SEATAC, Wash. — Washington already has the highest state minimum wage in the country, at $9.19 an hour. Soon, voters in this tiny city south of Seattle will decide whether to push the local minimum even higher.

If a majority of the voters here say yes to a referendum known as Proposition 1 when their mail-in ballots start arriving this week, a minimum wage of $15 an hour would be required for many businesses in SeaTac, more than twice the federal minimum of $7.25.

The measure would lift wages for thousands of workers at one of the nation’s busiest airports, Seattle-Tacoma International, which is within city limits. But business and labor leaders say the economic and political implications, with local democracy going where state and federal legislators mostly fear to tread, could be equally profound.

In an era in which organized labor mostly plays defense, unions targeted SeaTac and managed the signature-gathering process that put Proposition 1 on the ballot, viewing it as a potential model for raising wages and mobilizing workers in other parts of the country.