If Plaid Cymru does not seize leadership now, it will be harder for them to do so in the future. Likewise, if people vote against a Brexit, the SNP and Ukip lose the opportunity to use the results as a platform to launch their next electoral campaign on. If people vote to remain in the UK, the SNP and Ukip will have to play on the par with traditional parties, where the asymmetry of power is significantly tilted against them.
So they are an array of tactics open to unions over and above the open defiance of striking officially where the new thresholds have not been met. But it will mean unions thinking outside their comfort zones and boldly stepping into unchartered territory. Whether they will do so or not will be a key test of their mettle and ingenuity.
Listen to the seldom expressed left-wing arguments for leaving the European Union, because there are lots of things that are wrong with the EU that are not often publicised in the mainstream media. Remember that the likes of Tony Benn did not approve of the European Union, and that you have no obligation to approve of it either.