The suit, filed Thursday in King County Superior Court, alleges Seattle and King County violated the State Environmental Policy Act (SEPA) by signing the memorandum of understanding with investor Chris Hansen for the $490 million arena.
The union alleges the memo is itself a proposal that fixes the arena site and should have been submitted to the environmental review process, including a careful study of alternative sites.
"These provisions will create irreversible political momentum in favor of siting the proposed new arena on the Sodo site in the SEPA review process, making the SEPA alternatives and impacts review process a sham," said Cameron Williams, president of ILWU #19, in a statement.
The suit asks the court to invalidate the memorandum and order the city and the county to come up with a revision "that does not make the arena site in Sodo a foregone conclusion," the union said.
The union had said it would file the suit if Seattle Mayor Mike McGinn and King County Executive Dow Constantine signed a memorandum of understanding with investor Chris Hansen for the $490 million arena. The document was signed on Tuesday.
Union leaders denied allegations that the lawsuit was just a delaying tactic to stall the arena plan.
"ILWU is not against a new arena or bringing back the NBA to the Seattle area but we are not going to sit idly by while this arena and entertainment district, along with the traffic already generated by Safeco Field and Century Link Field, destroy the great working class jobs provided by our port and industrial area," said Williams.
Building another sports venue in the Sodo area will erode maritime, manufacturing and warehousing businesses and threaten the livelihood of union and other workers, the union said.
But King County Council member Joe McDermott said the county and city fully intend to look at alternative sites using proper procedures spelled out under environmental law.
"The county and the city together have done careful diligence and a thorough review of the proposal, and it includes a full environmental statement, including a comprehensive traffic impact analysis and study of alternative sites, and we've added an economic impact analysis as well," he said. "I believe we have solid information coming back to the council to make good decisions, and we're poised for our vote on Monday."
Seattle City Attorney Peter S. Holmes said approval of the memorandum of understanding would launch a thorough vetting process of multiple factors, not preordain that any complex will be built in the Sodo area.
He said the memo mandates the completion of "a full SEPA review, including consideration of one or more alternative sites, a comprehensive traffic impact analysis, impacts to freight mobility, port terminal operations and identification of possible mitigating actions, such as improvements to freight mobility, and improved pedestrian connections between the arena and the International District light rail station, the Stadium light rail station, the Sodo light rail station and Pioneer Square."
Also required as part of the SEPA review, Holmes stressed, is consideration of "a 'no action' alternative and an alternative site at Seattle Center."