The U.K. has been inundated with requests for permits giving truckers unimpeded access to the European Union in the event of a hard Brexit, highlighting mounting fears among hauliers that their business could be curbed.

Britain’s Department of Transport has received more than 11,000 applications for the 984 passes. The so-called ECMT permits weren’t meant to be a backstop for a no-deal split, having been created to help EU nations trade with neighbors like Turkey and Ukraine, but may end up as a last resort for U.K. truckers to range freely within the bloc if negotiations don’t bear fruit before March 29.

While the focus of concern about potential disruption to vital supply chains has been on customs delays at Dover, Britain’s biggest ferry port, truckers say they’re equally anxious that a backstop deal meant to safeguard trade in a no-deal scenario would limit their operations on the continent.

“Our members are getting many very concerned calls from their customers asking them if they are in the position to deliver on their contracts after March 29,” said Sarah Laouadi, policy manager at the Freight Transport Association, which represents firms that own more than half of the U.K. trucking fleet.

Because of the limited trade flows and length of journeys between Britain and locations beyond the EU for which the ECMT permits were originally distributed, only a relatively small number were ever issued, though the government might be able to increase the total from next year.

The DfT is distributing the passes based on how many international trips a company made in the past 12 months and what percentage of its business is international. A further 2,832 short-term permits will start to be allocated by March, a spokesman said by email.

The outline backstop agreed between the U.K. and European Commission would run for the nine months from March 29 through the end of the year. While the deal pledges to maintain basic connectivity, U.K. hauliers say it will limit their ability to deliver and pickup goods in a range of countries on the same trip, or even make multiple stops in the same country.