The 900-member Office Clerical Unit of the ILWU Local 63 called the strike after their previous three-year contract expired July 1.
The union's decision to return to work came after a labor arbitrator twice ruled their walkout was not "bona fide." Union officials say they are appealing the arbitrator rulings of July 1 and July 9.
A union representative said the decision to return to work was made to protect members' jobs from being outsourced. A representative from the shipping companies says he's wary about allowing the workers back on the job without a contract.
Union officials warn another walkout is possible.