The King County Labor Council failed to endorse any candidate for Seattle mayor after a contentious two-hour meeting Wednesday night. The council’s executive board earlier in the day recommended a dual endorsement of Mayor Mike McGinn and state Sen. Ed Murray, but the motion failed to win the needed two-thirds support from the assembled delegates.

Delegates did approve a dual endorsement of Seattle City Councilmember Mike O’Brien and challenger Albert Shen.

The executive board could recommend a sole endorsement for mayor at the next Labor Council meeting Sept. 19, said David Freiboth, executive secretary. The last time an incumbent mayor failed to pick up the Labor Council endorsement was when Paul Schell sought re-election in 2001.

Not choosing one candidate effectively neutralizes the resources of the Labor Council. Individual unions are still free to mobilize their members in behalf of Murray or McGinn.

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Both candidates have picked up endorsements from local affiliates, leaving no clear front-runner for labor in the race. McGinn has the support of the activist unions Unite Here Local 8, which represents hotel and restaurant workers, and the Machinists union; while Murray has the backing of several maritime and construction unions.

The Labor Council stayed out of the crowded primary because affiliates were divided among the top four candidates: McGinn, Murray, former Seattle City Councilmember Peter Steinbrueck and Councilmember Bruce Harrell.

Lynn Thompson: or 206-464-8305. On Twitter @lthompsontimes