Services will begin running on the Edinburgh to Tweedbank route in 2015 for the first time in 45 years, but lobby group the Campaign For Borders Rail has raised concerns the line could use older diesel trains.
Its officials have urged the Scottish Government to ensure the interiors are upgraded to match the standard of inter-city services.
Simon Walton, the group's chairman, said: "We had hoped to see the inter-city Class 170 units deployed on the Borders Railway, but it would appear 158s are now to be used.
" If that is the case, it is essential these are properly refurbished like those serving the scenic Highland routes. That means brighter interiors, appropriate luggage space and bicycle facilities, and a good seat-to-window match to allow the scenery to be fully appreciated by visitors.
"First impressions will be crucial for passengers who are new to rail."
The winning bid for the new ScotRail franchise is due to be announced in September or October. Abelio, Arriva, First, MTR and National Express are in the running.
A spokesman for Transport Scotland said it was for bidders to decide which stock to use.
He said: "Our requirements for the next ScotRail franchise, due for renewal next year, will see more comfortable trains throughout the Scottish network.
"We have not specified a particular class of diesel multiple unit for the delivery of Borders Railway services. This is for bidders to propose in line with our specification."