News of the move has enraged union leaders, whose relationship with the firm has already hit a new low amid a series of industrial disputes that have included the cancellation of most Sunday trains for five months.
Abellio, which will be stripped of its contract three years early next March, is giving new trousers, polo shirts, dress shirts, ties, and “softshell” jackets to nearly 4,000 staff including drivers, conductors and cleaners.
The company said it was “moving away from the classic suit-based uniform which included shirt, tie, waistcoat and blazer, to a more modern and contemporary look”.
But the change comes despite Abellio delaying the introduction of new uniforms for months when it took control of ScotRail in April 2015 to provide time to consult staff to ensure it met their approval.
An internal memo at the time stated: "We can’t roll a uniform out earlier than autumn if we want to be sure of getting it right, and we can only do that by engaging with you, the wearers."
The delay meant staff were told to snip the logos of previous operator FirstGroup from their uniforms or turn hats inside out to hide the old branding.
FirstGroup had provided new uniforms in time for the start of its franchise in 2004, as did Serco when it took over Caledonian Sleeper at the same time as Abellio started running ScotRail.
Abellio justified the delay in 2015 by insisting: “New uniforms have not been issued for day one because we are engaged in a thorough consultation with staff across the network to ensure the final designs are attractive, practical, and suitable for all working conditions.”
However, the firm has now admitted to problems.
It said: “Conductors told us that operating the opening and closing of train doors currently means either wearing a heavy waterproof coat that's too bulky for comfort or working in a soaked suit jacket.
"The new softshell jackets are showerproof and much more practical.”
Mick Hogg, regional organiser for the Rail, Maritime and Transport union, which represents conductors, said: “ScotRail are not being kind with the truth.
"They are spinning lies and creating fabrications - that full consultations took place on new uniforms.
"RMT are not happy with this further blatant disregard for our industrial relations.”
Kevin Lindsay, organiser in Scotland for train drivers’ union Aslef, said: “Uniforms are a hot topic and always have to be agreed, but yet again Abellio can’t just be truthful about their actions.
"The only saving grace from this latest sorry saga is staff are getting replacement uniform parts and the new supplier will be Scottish [Glasgow-based CKL].”
ScotRail uniform project manager Joanne Miller said: “Wearing a smart uniform has been part of being a railway worker since the days of the old British Rail.
“But sometimes the clothes haven’t been as practical and up to date as staff would have liked.
“We’ve really listened to what our colleagues have had to say and we are confident the new look will fit the bill perfectly as we continue to modernise our railway for the future.”