Union activists are to issue a "hands off Jeremy Corbyn" message to Labour MPs who are accused of undermining the party leader.
Mr Corbyn received a rousing reception when he addressed delegates at the annual conference of the GMB in Bournemouth yesterday, speaking up for workers' rights and attacking inequalities in the workplace.
Delegates are due to discuss a call for deselecting any Labour MP who refuses to give an undertaking to support Mr Corbyn.
A motion before the conference today "deplores" Labour MPs who are "deliberately sabotaging" the work of the Opposition.
The union's Ripon and Thirsk branch will call for a "clear and unambiguous" commitment from Labour MPs not to destabilise the party.
Other motions resolve to give Mr Corbyn full support.
The Labour leader has backed many union campaigns, such as a higher national living wage and public inquiries into the blacklisting of construction workers, the Hillsborough disaster and the clashes between police and pickets at Orgreave during the miners' strike.
He has addressed several union annual conferences in recent weeks.