The union sent a 72-hour strike notice to Westshore on Wednesday.
The company and union have been negotiating for several months over a new collective agreement after a previous agreement and two others expired Jan. 31.
The terminal is a key export center for miner Teck Resources.
Neither Westshore nor Teck were immediately available for comment.
(Reporting by Sabahatjahan Contractor in Bengaluru. Editing by Lisa Shumaker).