I think that given the #labour party can't even bring itself to express any support for striking unions these days all the unions really ought to withdraw funding from them.
Why would a union give any cash to a party which clearly supports the bosses over the workers in a pay dispute when profits are up and inflation is up and real wages are down.
I'd quit a union that was giving my money to this party frankly. Waste of cash on just more neoliberal wankers.