The RMT union has called on the Scottish Government to set out an immediate timetable for Abellio to be stripped of its ScotRail franchise.
The transport workers’ union claims performance by the operator has slumped and not enough money is being invested in staffing, services and safety.
The demand comes on the eve of a day of protests organised by the union in support of a campaign for “Safer Scottish Railways”.
ScotRail said the comments do not stand up to scrutiny and added that it is investing hundreds of millions of pounds on new trains and systems.
Almost 20,000 people have signed a petition calling on Transport Minister Humza Yousaf to “make ScotRail bosses improve Scotland’s trains or strip them of their contract”.
ScotRail was recently fined £483,000 for failing to meet required standards for trains and stations.
First Minister Nicola Sturgeon last week indicated that stripping ScotRail of its contract to run the railways is on the table if performance fails to improve.
RMT general secretary Mick Cash said: “RMT is campaigning to make Scotland’s trains safer, more secure and accessible.
“This can only be done with a publicly-owned service where profit isn’t the main motive of the operator.”
He added: “RMT calls on the Scottish Government to set out a timetable for bringing ScotRail under public ownership, and with the current level of anger that’s reinforced in the petition there can be no excuse for the dragging of heels.
“The union is available for talks with ministers to take the issues of safe staffing, investment and public ownership forwards.”
A ScotRail spokesman said: “These comments bear no scrutiny whatsoever. Performance has dipped by around 1% – but is still tracking around the 90% mark – and we have a robust performance improvement plan to rectify that.
“At the same time, we are investing hundreds of millions of pounds on new trains, refurbishing our existing fleet and introducing queue-busting smart technology to keep people moving.”
Dutch firm Abellio was awarded the franchise in 2015 for 10 years but ministers can strip the company of the contract after five years if punctuality falls below 84.3%.