A new UK levy on road hauliers from the Republic of Ireland entering Northern Ireland could put small firms out of business, an Irish TD (MP) has claimed.
Hauliers going to Donegal through County Tyrone or travelling on other arterial routes must pay around £10 a day.
The charge is primarily aimed at European goods carriers.
British and Irish parliamentarians want an exception to be made for Northern Ireland travel.
They made their call at a British Irish Parliamentary Assembly (BIPA) meeting in Ashford, Kent, on Tuesday.
Joe O'Reilly TD, who represents the Irish border constituency of Cavan, said: "I cannot stress how grave the impact of this is and how many jobs are at stake.
"This levy is totally prohibitive, it is terminal for them in many respects."
The road user levy for heavy goods vehicles (HGV) weighing 12 tonnes or more, was introduced by the UK Department of Transport in April.
It is aimed at ensuring these vehicles make a contribution to the wear and tear of the road network.
The cost varies according to the vehicle's weight and how long it is on UK roads.
The levy can be paid by day, week, month or year and discounts are available for longer periods.
According to the Transport Department, the introduction of a charging scheme for foreign hauliers is something the logistics industry has long called for, provided that the cost burden on UK carriers remains roughly neutral.
But some members of the BIPA called for an exception to be made for Northern Ireland.
Irish BIPA members expressed particular concern over the A5 route that connects Dublin and the Irish midlands to Donegal via counties Tyrone and Londonderry.
The vice chairman of the BIPA, Robert Walter MP, said sometimes lorries did not stop in Northern Ireland but passed through it several times a day during the course of their business.
Fine Gael TD Mr O'Reilly claimed many small haulage businesses in his constituency operated on the tightest of margins.
Irish Senator Jim Walsh said MPs should be looking at "an all-island economic model".
"It is in the interests of people north and south that we have that, there should be free movement of EU goods north and south," he said.