A union boss has accused Rishi Sunak of "silly posturing" instead of working to resolve industrial disputes across the country.
Sharon Graham, general secretary of Unite, today condemned reports the UK Government is planning to fast-track laws which will restrict workers' ability to strike.
The Tories are considering measures which could allow employers to sue unions and sack workers if they did not provide a certain level of service.
SNP MP Mhairi Black branded the plans "immoral".
It comes as rail services are being crippled by a third consecutive day of industrial action, with about 12,500 train drivers from 15 companies striking over pay across the country on Thursday, following a 48-hour picket by the RMT.
Cross-border rail services between Scotland and England are currently severely disrupted due to strike action by members of the Aslef union.
Avanti West Coast, TransPennine Express and CrossCountry said they are not running services on their routes on Thursday.
Graham said: "Yet again, Rishi Sunak abdicates his responsibility as a leader.
"Instead of silly posturing and game playing, he should step up to the plate, act as a leader and start negotiating to resolve the crises his government has created.
"The game is up – everyday people can see through the Tories’ web of lies. They can see that this government is not interested in ensuring that workers and communities get their fair share. This is a government for the rich and powerful.
"Whatever the latest scheme the government comes up with to attack us, unions will continue to defend workers."
Mick Whelan, Aslef general secretary, warned that legal limits on how many workers can take time off to picket could mean unions launching longer strikes to retain the same impact of day-long action under current rules.
And he said it was "inevitable" that further strikes will be held unless there is a breakthrough to the long-running row over rail workers' pay.
He said: "The situation is getting worse and my members now want to go harder and faster because of the lack of progress.
"We are in a weird world where the Government will do anything to keep private companies in the industry.
"It is inevitable that more strikes will be held and probably escalate.
"The train companies say their hands have been tied by the Government. While the Government – which does not employ us – says it’s up to the companies to negotiate with us."
Reacting to the anti-strike plans, SNP MP Black said: "These immoral proposals from the Tory government speak to the hard-right rhetoric that has Westminster in a choke-hold - and it's Scotland's key workers who are set to pay the price of Westminster control.
"Just months ago, the UK government applauded key workers - now, they are threatening them with the sack if they go on strike. It's utterly shameful.
"The SNP condemns these plans in the strongest possible terms, which contrast starkly with the constructive role the SNP Scottish Government has played in recent pay disputes north of the border."
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