Mediation call in Rhondda Cynon Taf council job talks
A union which says council workers are facing dismissal unless they sign up to new contracts is seeking mediation through the conciliation service Acas.
The GMB said Rhondda Cynon Taf council (RCT) was seeking to impose worse pay and conditions, and consultations were a "tick box exercise".
The union said it would "not engage in dialogue" with the council while the threat of a "lock-out" was in place.
RCT said the Section 188 notice was issued to allow consultation to begin.
The union said it wanted the lock-out "threat" - dismissal unless workers sign new contracts - to be lifted before talks could continue.
Gareth Morgan, the GMB regional officer, said: "Following a meeting with the joint trade unions, the GMB have reluctantly decided to continue our boycott of talks, with the support of Unite trade union whilst we take further guidance.
"In an attempt to resolve this impasse we have decided to seek the good offices of Acas to ask them to mediate in an attempt to find a way forward for us to be able enter into meaningful negotiation without duress."
The council has said that as a result of pending cuts to public sector funding, it was likely to face a funding shortfall of around £60m over the next three years.
It said the new terms and conditions for staff would avoid the need for compulsory redundancies, protecting hundreds of jobs.