Workers had been due to go on strike for 24 hours on Monday but the Public and Commercial Services (PCS) union has been forced to cancel this action.
"We will be telling members about our future plans for action on April 8," said the PCS in a statement to members. "This is likely to contain an escalation of our original plans to cause maximum disruption to the employer.
"We recognise that the employer’s use of anti-trade union laws will frustrate members but there will be more opportunities for you to demonstrate your anger at the attacks on hard working staff and the attempts to cut your terms & conditions, jobs and pay."