Car manufacturers across the United Kingdom have started to trigger contingency plans as fears of a ‘no deal’ Brexit grow.

Reuters reports that many car companies building vehicles across Britain are revising production schedules and stockpiling parts before Brexit is triggered on March 29. While British Prime Minister Theresa May is looking to avoid tariffs and trade barriers with the European Union, many have been critical of her plans.

In response, McLaren is investigating having its vehicles certified by both British and EU agencies to smooth sales. Additionally, it will stockpile critical components and make alterations to its EU shipments around the time of Brexit.

Elsewhere, a spokesman from BMW stated that the carmaker is currently looking for lorry parking areas and warehousing on both sides of the English Channel and wants to lease certain storage locations. Additionally, expensive IT systems are being developed to deal with the tens of thousands of new documents which could be needed if tariffs and custom changes are made.

Numerous British automakers are also asking key suppliers to look into how they will handle potential delays at ports. Many UK plants rely on the just-in-time delivery method to cut down on costs and accelerate production.

Jaguar Land Rover has previously warned that it could be forced to shut down its British facilities if a no deal Brexit occurs. According to a spokeswoman, the company is keeping its options open and hasn’t made any final decisions.

It’s not just carmakers producing vehicles in the UK that will be affected. European manufacturers who import vehicles in the UK are also facing some uncertainty.