Two heritage railways fear government measures to limit the burning of coal could affect their ability to operate.
The Department for Environment, Food and Rural Affairs (Defra) wants to ban the burning of household coal by 2025.
The lines in North and West Yorkshire say they could have to import coal, which would be prohibitively expensive.
A Defra spokesman said: "Air pollution is a significant threat to public health and the government has a duty to take action."
The North Yorkshire Moors Railway, which runs steam engines between Pickering and Whitby, said the proposed ban was a "significant threat".
The Keighley & Worth Valley Railway runs on five miles of track and was used in the film, The Railway Children.
Both railways believe the domestic coal ban would make mining it commercially unviable in the UK and they would have to turn to foreign imports at a much greater cost.
Chris Price, the general manager of the North Yorkshire railway, said they were looking at Russian coal.
"If we are forced to go abroad, if the domestic coal ban comes in to the UK, that perhaps the government would consider giving a financial subsidy to make sure the cost of coal was kept down," he added.
Keighley MP John Grogan said the Keighley & Worth Valley Railway was "crucial to tourism".
He said: "I hope the government will live up to the promise they made that they will provide an exemption for heritage railways from the air quality regulations they are going to bring in."
The Defra spokesman added: "We understand how important our nation's heritage railways are and the sector raised a number of issues in our consultation."