Environment: Fear for future of north Wales steam trains if coal banned
There are fears steam trains will stop running under new laws which may lead to a ban on burning coal.
Paul Lewin, of the Ffestiniog and Welsh Highland heritage railways in Gwynedd, said the industry needed "water-tight" exemptions to any proposed legislation.
Concerns were raised in the House of Lords any new law could "bring about the death of Thomas the Tank Engine" and threaten heritage attractions.
A committee was told heritage vehicles were not included in the legislation.
Baroness Bloomfield of Hinton Waldrist said the UK government was "not doing anything that would impact on heritage vehicles, nor would they plan to do anything that would".
"An exemption is just not needed because these are not caught within the scope of the bill," she added.
But Mr Lewin fears heritage lines could become the victims of "unintended consequences".
He said: "If the legislation is not shaped in a way that accommodates heritage, then we could be in big trouble.
"I think it would be good to make the point that they've got to make sure that the law does make an exemption for heritage railways."
The Ffestiniog and Welsh Highland heritage railways, which link up at Porthmadog Harbour station, run for a combined 40 miles and attract about 200,000 visitors each year.
Together, the lines, which terminate at Blaenau Ffestiniog and Caernarfon respectively, make up the longest heritage railway in the UK.
A total of 25 steam engines run on the lines, while Mr Lewin estimated there were between 60 and 70 engines in use across Wales, with most only used "from time to time".
He added: "In terms of coal consumption, it's a microscopic amount compared to all the other things that are consuming fuel."
Speaking during the bill's committee stage, Conservative peer Baroness Neville-Rolfe, said she feared "an error could be made" and heritage vehicles could be consigned to a "sad death".
She said: "It matters because this bill could bring about the death of Thomas the Tank Engine and his... nautical steamboat equivalent."
Labour peer Lord Faulkner of Worcester said he wanted ministerial assurance heritage vehicles would be "permitted to continue to burn coal".
Meanwhile, Liberal Democrat peer and former railwayman Lord Bradshaw said areas such as north Wales would be "immeasurably harmed" if steam locomotives were banned.