"There seem to have been a number of problems which came to light after the last dispute," said GPMU national industrial officer Peter Ellis.

These are believed to concern the non-payment of additional pay made to workers for working different shifts. Ellis said workers were currently forgoing these additional payments.

However, Euro Packaging joint managing director Shabir Majid said he had agreed a deal in June for discussions on pay reviews to commence in January.

Majid said the GPMU wanted to start negotiations now and was looking to impose a 30% pay increase and 20% bonus rise.

He said that things had progressed at EP since the GPMU had been recognised there.  He said that while happy with the move, he failed to understand why the union was now "looking to move the goalposts".

Ellis was hopeful that industrial action could be avoided. ACAS has now been called in. Earlier this year staff went on strike over the threat of 100 of the 170-strong workforce being made redundant, in the end 80 were let go.

Story by Andy Scott and Josh Brooks