The railway track through Troon is due to reopen on Friday, six days after a serious fire severely damaged buildings at the Ayrshire station.
Although the track is set to reopen on Friday, no train services will stop at Troon, where engineers are continuing their work to make the structures safe.
The RMT said it had written to Chief Inspector of Railways Ian Prosser on Thursday, calling for answers about whether the extensive damage and travel disruption "could have been avoided had Troon station been properly staffed".
Today a union chief said cost-cutting and reduction of staff by private rail firms could have played a part in the disruption.
RMT general secretary Mick Lynch said: "The devastating fire at Troon station shines a light on just how dangerous the rail industry's plans to de-staff our stations are.
"Station staff play a vital role in helping deliver a safe, secure and accessible railway and it is long overdue that this cost-cutting, profit maximising measure of de-staffing our stations and trains by privatised train companies and the rail industry was stopped in its tracks due to glaring and serious health and safety risks.
"Today I have written to the Chief Inspector of Railways demanding he launch an urgent investigation into the Troon Station fire and the wider programme of de-staffing our stations which is only likely to accelerate due to the Government's and privatised rail industry's cuts agenda."
Liam Sumpter, Network Rail route director for Scotland, has said engineers are working to make the station safe and that investigations into the cause of the fire are ongoing.
He said: "The damage caused by Saturday's fire was extensive and we must make sure we have carried out all necessary safety checks, and made vital repairs, before we can run trains through this section of track.
"We are working intensively to restore services as quickly as we can on both the overall line and for Troon-based passengers."