A strike is on the cards at Lyttelton Port as workers are unhappy with their safety concerns being ignored, and roster changes without consultation.

It comes after 21 meetings between Rail and Maritime Transport Union and Lyttelton Port Company since July 2017.

The port is wanting to change rosters to operate around the clock, although no fatigue management policy is in place.

Union organiser John Kerr says accidents can happen quickly so safety measures need to be in place.

"Fatigue is a big issue on the waterfront and our guys are operating heavy machinery so those rosters, those hours of work have to be done in a safe manner."

He says going on strike is the last option but it will go ahead if necessary.

"We'd like to sit down with the company and sort out a deal. We have to give two weeks notice of industrial action anyway so there is a period there where we are willing to get around the table and try and knock something out."

Workers are ready to begin industrial action from the third of March.