German regulators are urging clinical trial sponsors in the UK to designate new, European-based representatives as Brexit’s March 29 deadline draws near.

Some 1,300 trials are operating with a UK-based representative and may have to stop their work if Britain leaves the EU without some kind of new regulatory regime in place, said German’s Federal Institute for Drugs and Medical Devices in a new advisory.

German regulators are warning trial sponsors that changing a representative requires “substantial amendments” to a trial’s regulatory regime. Sponsors should file a single amendment focused on their post-Brexit move to the continent and let any other regulatory questions lie for now. It will probably take between 20 to 35 days to process the new filings, the institute says.