Workers at DBC food service's Dundonald site went on strike this week for the second time this month.

The 24-hour walkout, on Tuesday, followed a four-day stoppage over a new contract that would increase the hours staff worked from 37.5 hours to 45 hours a week for no extra pay.

DBC said it did not miss a single customer's delivery during the previous strike from 9-13 June, due to "robust contingency plans".

However, the GMB officials are angry that DBC hired agency workers during the strike. GMB senior officer Mick Conroy wrote to three agencies last week to remind them of employment regulations, which state that agencies should not supply workers for duties normally carried out by a worker who is taking part in a strike.

DBC had tried to sidestep the legislation by having its drivers, who were not on strike, work in the warehouse and hired agency drivers to cover for them, GMB officials claimed.

DBC said it had acted completely within the law and did not use agency staff to cover the jobs of those on strike.

The changes were part of a process to harmonise the terms and conditions across the company following acquisitions made before 2009 and that most of its 1,000 staff had accepted the new contracts, it said.