Concerns over the impact of tolls on businesses using the two Severn motorway crossings have been given to MPs.
Haulage and business leaders called the tolls "gratuitous," in evidence to the Welsh affairs committee.
But Severn River Crossing said tolls were set by Parliament.
A report into the economic impact on small businesses found a bigger impact on firms in south Wales compared with Bristol.
The findings were made by Professor Peter Midmore from the School of Management & Business at Aberystwyth University who led the study.
He told the hearing that of businesses that weren't affected by the tolls, a greater number were on the Bristol side.
Ian Gallagher, policy manager for the Freight Transport Association (FTA), who gave evidence at the hearing at the House of Commons, said afterwards that tolls should be reduced.
'Pain in the backside'
"Severn tolls are the highest in the UK and simply unsustainable for many companies that use this vital trade corridor," he said.
Denise Lovering, director of Glenside Commercials, a vehicle maintenance company in Caerphilly, told the hearing Welsh companies were taking an "unfair hit".
She said that in a perfect world, there would be no tolls at all, but that her biggest fear was that when it reverts back to public ownership in about 2017, it could be seen as a "cash cow".
Discussing the on-going problem with toll booths unable to accept payments by credit card, she said it seems "antiquated to me in this day and age" and a "pain in the backside".
Swansea West MP Geraint Davies said the absence of credit card facilities sends a sign that "Wales is not open to business and that we're a little bit backward".
In addition to the tolls and their economic impact, the Welsh affairs committee is examining the future of the bridges after the crossings have reverted to public ownership, their condition and maintenance costs.
Currently operated by a private company, the Severn Bridge will return to government ownership when the firm has collected a fixed sum of money from tolls.
Jim Clune, general manager of Severn River Crossing, explained that the Severn Bridges Act 1992 set out the toll levels which were amended each year based on the Retail Price Index.