Caledonian Sleeper workers are taking their place on picket lines across the country amid an ongoing dispute about pay and conditions with operator Serco.
The RMT union said its members are taking industrial action on Friday and Saturday.
The union’s general secretary Mick Lynch claimed staff had been “left out in the cold” as he demanded a “fair deal” for rail workers who have gone on strike.
He said: “It’s a scandal that Serco and their political paymasters in the Scottish Government are leaving the sleeper staff out in the cold.
“There will be no sleeper services back to London from COP26 and the responsibility for that lies fairly and squarely with the company and those holding the purse strings.
“There can be no climate justice without workplace justice and it’s time for a fair deal for the Caledonian Sleeper staff. The union remains available for further talks.”
Lynch said the union remained willing to take part in further talks.
On Wednesday, the union said the most recent offer of a 1.4% rise from the company, which is below both inflation and a deal agreed for ScotRail workers, had been overwhelmingly rejected by members.
Pickets were out at key locations of the route overnight, with lines set up in London, Glasgow, Edinburgh and Inverness.
Jeremy Corbyn, the former Labour leader, also joined the picket line in Glasgow and spoke in support of the strike action.
In response to the strikes, Serco said it will be cancelling all Highland services on November 11 and 12, while the Caledonian Sleeper service will run southbound from Glasgow and Edinburgh to London Euston on Friday and return northbound the following day.
The train operator and Transport Scotland have been contacted for comment.