The dispute between Lyttelton Port Company and its striking workers is becoming increasingly acrimonious.

Port workers are back on the job this morning but will strike again for three weeks next month if they can't reach a deal over pay and conditions.

Christchurch City Holdings Limited owns the port but has previously refused to get involved in the dispute, saying it's up to the company and union to reach a deal. 

But Rail and Maritime Union spokesperson John Kerr is warning pending strikes will have a huge impact on the Canterbury economy.

"This is having an impact on the Canterbury economy and on the livelihoods on hundreds of thousands of decent, hardworking Cantabrians."

The council has previously refused to get involved in the dispute -saying the matter needs to be resolved by the company and the union.