Common Sense SeaTac, a business-backed group that opposed the initiative, announced Tuesday it is requesting a recount.
The initiative, which would require a $15 minimum wage and a handful of paid sick days for about 6,500 workers, was poised to pass by 77 votes out of 6,001 counted. The election results were scheduled to be certified Tuesday afternoon.
Under election rules, a group can request a recount from King County if it covers the costs.
"When an election is this close, everyone should be assured the outcome is as certain as possible," Common Sense SeaTac co-chairman Scott Ostrander said in a statement. "If there's one thing we all learned from the 2004 recounts of the governor's race, counting ballots has a margin of error like any other human endeavor. And we learned, too, recounts can change the result. So we are asking for a hand count of the ballots to get the most accurate possible count."
The recount request is expected. The SeaTac measure drew some $1.8 million in campaign spending in the small city, with national labor groups supporting the initiative and national business groups opposing it.
Backers of the initiative declare victory Tuesday at a news conference at Seattle-Tacoma International Airport. It's the second time the group has declared victory; they held an election night celebration before their 261-vote advantage began to shrink.
Washington has the nation's highest state minimum wage at $9.19 an hour; the federal minimum wage is $7.25 an hour.
The proposition is also facing a court challenge, led by Alaska Airlines' owner, Alaska Air Group Inc. The airline is challenging whether an initiative can give the city authority over the airport, which is operated by the Port of Seattle.