Melbourne's busy container port will be forced to a standstill on Wednesday when tugboat engineers walk off the job.

The strike comes amid an escalating national fight between the engineers and their employer, Svitzer Australia, which runs tugboats at several east-coast ports.

Tugboat unions are pushing up against Australia's biggest miner. Credit:Jessica Hromas

Strikes have already halted port activity in Geelong, Sydney and Newcastle this week. But Wednesday's 12-hour strike in Melbourne is expected to have the biggest impact.

From midday to midnight, delays will plague the Port of Melbourne because tugboats that tow commercial carriers and tankers will be inoperative.