The Railways Policing (Scotland) Bill would integrate the current force overseeing Scotland’s railways - British Transport Police (BTP) - with Police Scotland.
Transport workers’ union RMT warned those backing the Bill are putting rail passengers and workers at an increased safety risk while Labour plans to vote against it and has called for it to be scrapped, saying it could lead to railway strikes.
Transport minister Humza Yousaf said the service would be “enhanced”.
Speaking ahead of the stage one debate on Tuesday, Scottish Labour’s justice spokeswoman Claire Baker said options for devolution of BTP functions had not been fully explored by Parliament and raised concerns over cost.
She said: “There are clear operational and serious financial questions that remain unanswered by the Government.
“We already have in Scotland a transport policing system that works and serves us well, but this Bill risks that.
“With concerns over the financial memorandum attached to this Bill, this could prove to be a costly way to fix a problem that isn’t broken.
“With a Bill lacking a manifesto mandate and with the real prospect of strike action on our railways, the SNP must halt its plans and think again about the future of railway policing in Scotland.”
The Scottish Parliament’s Justice Committee gave majority backing to the Bill despite one Labour and three Tory MSPs withholding support.
RMT general secretary Mick Cash called on MSPs to oppose the Bill.
He said: “MSPs need to be clear that if they do not oppose this Bill in principle, then they will be increasing the risk to the safety and security of rail passengers and workers.
“The loss or erosion of specialist skills provided by the British Transport Police is opposed by rail workers, rail employers and the police federation.
“The Scottish Government’s consultation failed to include any alternative approach to that in the Bill.
“That is not a sensible, proportionate or safe way to proceed as four MSPs on the Justice Committee looking at this Bill have recognised.
“MSPs must put aside ideology and party loyalty, and oppose this Bill in the interests of safer Scottish rail services.”
Mr Yousaf said he expected the debate to be a “further step towards creating a more effective, joined-up police service on our railways” with the merger ensuring railway policing in Scotland is “accountable” to the people of Scotland.
He said: “Alongside Police Scotland, we have made clear that specialist railway policing expertise and capacity will be maintained and protected within the broader structure of Police Scotland, with improved access to wider support facilities and specialist equipment, providing an enhanced service provision to both the rail industry and the travelling public.”
He confirmed the government commitment for a triple lock on jobs, pay and pensions conditions of railway policing officers and staff in Scotland.