Labor unions and business groups spent a combined $2 million for and against a measure that would raise the minimum wage for some workers in SeaTac, Wash., a town of just 12,108 registered voters.

The ballot measure would raise the minimum wage for workers affiliated with SeaTac’s main attraction, the international airport that serves the Seattle-Tacoma region. Hospitality and transportation workers would be eligible for a $15 per hour minimum wage — by far the highest in the nation.

As of Tuesday night, the measure led by a narrow 54 percent to 46 percent margin, on 3,283 votes cast. Because Washington State uses all-mail-in voting, backers and opponents expect another 3,000 or so ballots to trickle in over the next few days, leaving the measurer’s fate very much up in the air.

Labor unions and their backers spent more than $1.4 million campaigning for the wage increase, according to filings made with the state Public Disclosure Commission. Several branches of the Service Employees union contributed more than $325,000 to the effort, while Working Washington, a coalition of labor groups, chipped in another $150,000 and the Teamsters union added $55,000.

Alaska Airlines, which is headquartered in Seattle and uses SeaTac as its major hub, spent more than $155,000 to oppose the measure. The American Car Rental Association gave $100,000, while a political action committee run by the state hotel and lodging association spent $109,000 against it. The Washington Restaurant Association, whose members would have to pay their employees at SeaTac under the new wage, also chipped in $60,000 against the measure.

Altogether, the two sides spent more than $170 per registered voter. If the turnout estimates are correct and 6,500 voters eventually cast ballots, that would add up to more than $318 per vote.

The amount spent is more than the two candidates who ran for mayor of Seattle, a city with nearly 40 times as many registered voters, spent on their own campaigns.