More than 2,600 drugs have some stage of manufacture in Britain and 45 million patient packs are supplied from the U.K. to other European countries each month, while another 37 million flow in the opposite direction.

Brexit threatens the free flow of these goods, given stringent medicine regulations that may require the retesting of drugs shipped across borders in the absence of an agreed trading arrangement.

The European Federation of Pharmaceutical Industries and Associations (Efpia) said a survey of its members showed 45% of companies expected trade delays if Britain and Europe fell back onto World Trade Organization rules after Brexit.

Drugmakers also face an additional hurdle when it comes to licensing their products, since more than 12,000 medicines will require a separate U.K. license in order for them to be prescribed.

“For life-saving and life-improving medicines, the EU and U.K. cannot afford to wait any longer to ensure that the necessary cooperation on medicines is in place from the day the U.K. leaves the EU,” said Efpia Director General Nathalie Moll.

Pharmaceutical companies have insisted since last year’s Brexit referendum that a comprehensive agreement is needed to ensure maximum alignment between EU and British pharmaceutical regulations.

But with the clock ticking down to Brexit in March 2019 with no sign yet that a trade deal will be concluded, many companies are now starting to draw up plans to protect drug supply chains, including building extra testing centers in Europe.