RMT members have approved more industrial action in a new ballot as part of their campaign for a no-strings pay increase.
The union has rejected a 1.4 per cent offer from the company.
The demonstration follows four walkouts which halted some Sleeper services between Scotland and London in October and November, including during the COP26 climate change summit in Glasgow.
The union told The Scotsman that more action could be called at any point following the endorsement for additional stoppages in the latest ballot, which is required every six months during a dispute.
General secretary Mick Lynch said: “Today’s demonstration sends a clear message to multinational corporation Serco that it cannot continue to deny these key workers pay justice.
"These workers have kept vital rail links running throughout the pandemic and they deserve a pay award that recognises their commitment and the soaring cost of living.
"Serco recently announced its first interim dividend since 2014 and boasted of ‘stronger than expected recent trading’.
"The Caledonian Sleeper franchise continues to be fully funded by the Scottish Government under its emergency measures agreement, which also permits the payment of fees to Serco.
"Serco could easily fund a proper pay rise for these front line workers, but instead it has preferred to line the pockets of its private shareholders.
"Enough is enough. RMT is demanding pay justice for Caledonian Sleeper workers.”
Serco described the dispute as “incredibly frustrating”.
Caledonian Sleeper managing director Kathryn Darbandi said: “We are deeply disappointed that the RMT felt it appropriate to go ahead with a ballot for further industrial action, at a time when a good pay offer was on the table.
"The outcome of this ballot merely raises the prospect of further disruption for our guests and will lead to further loss of earnings for our staff.
"It also undermines the reputation of Scotland’s railways further, at a time when we should all be focusing on our recovery from the impact of the pandemic.”