The TSSA union voiced its fears after Abellio ScotRail posted a loss of £3.5 million after tax in its first full year of running the service.
With transport minister Humza Yousaf working to enable a public-sector operator to bid for the franchise, TSSA general secretary Manuel Cortes said senior managers could be “in the process of awarding themselves big golden goodbyes before they pull the plug, whilst the SNP turns a blind eye”.
The union is also concerned the voluntary severance programme could impact on railway safety, depending on the number of staff who take up the offer.
Abellio, an arm of the state-owned Dutch railway operator Nederlandse Spoorwegen (NS), took over the running of the ScotRail franchise in April 2015 and made profits of £9.5 million in the first nine months.
However, in September it emerged it was loaned £10 million from Abellio Transport Holding - another branch of NS - last year.
Mr Cortes said: “ScotRail has just posted a big loss, so it beggars belief it can afford these payouts.
“It is likely the pay-offs will cost more than the profits Abellio have so far made out of the ScotRail franchise.
“So we have to ask just what is the game Abellio are playing with its workers, its taxpayers and the Scottish Government itself?
“Are senior managers in the process of awarding themselves big golden goodbyes before they pull the plug, whilst the SNP turns a blind eye?”
Mr Cortes added: “By this Friday the whole of Abellio’s management, clerical and administrative team have been asked to say whether they’d like to take voluntary severance at 70 per cent of their total pay cheque.
“If you’re on £18k a year, then even a £14,600 tax-free lump sum is an effective bribe to give up your job.
“If you’re one of the too many ScotRail fatcats earning £100k plus, then you are eligible for a minimum pay-off of £70k tax free.
“We are concerned the Abellio pay-outs will be paid by the Scottish taxpayer rather than Abellio.
“We want reassurances that everything will be done done to ensure safety-critical and rail journey delivery planning jobs aren’t axed.”
Scottish Labour transport spokesman Neil Bibby backed calls for the severance programme to be put on hold.
He said: “ScotRail’s severance programme should be put on hold while meaningful talks with the TSSA and the rail unions take place, and assurances should be given that jobs vital to the running of the railway and safety-critical posts will be protected.
“If ScotRail ignore the views of their workers and press ahead with this programme regardless, then SNP transport minister Humza Yousaf should intervene.”