Rail union boss Mick Lynch has revealed a top lawyer has advised him that the Tories' anti-strike laws are "completely illegal".
The RMT general secretary said plans by Rishi Sunak will make the British people "less free", "conscript our members" into work and curtail the right to strike.
Mr Lynch - whose members are on another 48-hour walkout right now - refused to rule out announcing more strike dates next week, if crunch talks on Monday do not resolve a dispute over pay, conditions and job cuts.