WASHINGTON (Reuters) - A port strike on the U.S. East Coast and Gulf of Mexico will go ahead starting on Tuesday, the International Longshoremen’s Association union said on Sunday, signaling action which could cause delays and snarl supply chains.

"United States Maritime Alliance ... refuses to address a half-century of wage subjugation," the union said in a statement. The United States Maritime Alliance, known as USMX, represents employers of the East and Gulf Coast longshore industry.

If union members walk off the job at ports stretching from Maine to Texas, it would be the first coast-wide ILA strike since 1977.

It was not clear if any negotiations were taking place or planned before the midnight Monday deadline.

Earlier, President Joe Biden said he did not intend to intervene to prevent a walkout if dock workers failed to secure a new contract by an Oct. 1 deadline.

"It's collective bargaining. I don't believe in Taft-Hartley," he told reporters. Presidents can intervene in labor disputes that threaten national security or safety by imposing an 80-day cooling-off period under the federal Taft-Hartley Act.

(Reporting by Costas Pitas, David Shepardson and Steve Holland; Editing by Leslie Adler)