The workers were due to return at 7am on Friday, following two separate nine-day lockouts by the company stretching back to February 18.

The third straight lockout means workers won't return until March 18 at the earliest.

In the notice of lockout sent to the coal terminal employees the lockout was in response to a review of "the level of disruptions to the operations of recent protected industrial action".

However, workers have not walked out on strike since February 15 and CFMEU southern district vice president Bob Timbs said the union had sent no notifications of industrial action since that time.

READ MORE: Explaining the coal terminal drama

Mr Timbs said, with a federal election in the coming months, the dispute could become a significant issue.

"This is going to turn into a political football," Mr Timbs said.

"If you have a look around the country, I don't know that there’s anything bigger and dirtier than this."

At the heart of the dispute is a union concern the terminal wants to have the freedom to sack workers and replace them with contract labour.

If a new deal is not reached by March 29, the current agreement is terminated and the basic award will take over.

"It appears what will probably happen is they will continue to lock out our members until the agreement terminates," Mr Timbs said.

"Then there’s no job security clause left, they could well move to terminate their employment and replace them with contract labour."

A spokeswoman for PKCT would not provide evidence of the "recent industrial action" it claimed as justification for the latest lockout.

Nor would she state the terminal had no plans to sack workers and replace them with contractors.

"The continuity of stable operations must be preserved during this period of industrial action, along with the ability to meet contractual obligations for outgoing ships," she said.

"PKCT has advised it will continue negotiations on the Enterprise Agreement."