The Scottish Passenger Agents Association has launched a campaign to protect direct trains between London and Scotland.
The SPAA lodged a "strongest possible protest" with the UK Department for Transport (DfT) against the withdrawal of direct rail links from Aberdeen and Inverness to London.
Direct trains on the routes may be under threat according to a recent government report.
In Sir Andrew Foster's report for the DfT, Review of the Intercity Express Programme, he looked at the next generation of trains for the UK to replace the aging diesel fleet.
Under previous plans, the new fleet would have bi-mode trains manufactured by Hitachi, which would mean where electric power was not available the train could use another energy source, such as diesel.
Foster's report questioned the reliability of the bi-mode trains, and suggested using electric powered trains where possible, with passengers transferring onto diesel powered trains on routes without electric power.
The Inverness and Aberdeen routes are not electrified, and according to Foster's report "may never be". He suggested the through-routes could be axed in favour of providing "better porterage, ensuring the physical proximity of appropriate onward connection trains, and guaranteeing to hold them."
But according to Kevin Thom, SPAA's vice president, such plans would "seriously undermine support for rail travel".
He said the proposal is "entirely inconsistent" with the Tory-Lib Dem coalition government's plans to improve regional rail services in a bid to reduce domestic air travel.
Business travellers in the north of Scotland already face lengthy connecting journeys to and from Aberdeen and Inverness, said Thom.
"Having to begin or complete their journey on trains which do not provide popular Intercity amenities such as wifi access, power points and comprehensive catering, will further erode support for long-haul rail travel. They will simply take to the air," he said.
Thom called for "genuine and extensive consultation before any such erosion of vital direct rail services takes place".
"Far from undermining the existing long-haul rail network in the UK, the government should be contributing to the electrification of the lines between central Scotland and the North," he said.
www.dft.gov.uk www.spaa.org