The UK's large legal services sector warns it could be at risk if the government fails to secure guarantees for it after Brexit.
A new report by lobby group TheCityUK says the £26bn sector will suffer if it loses "mutual enforcement" rules.
These require EU member states to recognise and enforce each others' law.
It says losing this would make the UK a "less attractive" place for global businesses to resolve legal disputes and draw up commercial contracts.
The group is asking the government to find a regulatory alternative that will allow this mutual enforcement to continue, or risk degrading the "primacy of English law".
TheCityUK also wants to retain the free movement of people for the legal profession.
The report says the UK legal services sector employs 370,000 people. More than 200 foreign law firms operate in the UK and employ in excess of 10,000 people.
It says the sector will suffer disproportionately if its clients - financial services, technology, telecoms, energy and property firms - find their businesses negatively affected by Brexit.
The banks' industry lobby group, the BBA, has voiced a number of warnings about the potential damage to its business by Brexit. It has warned several may pull out of the UK altogether if Brexit affects their ability to do business.
TheCityUK's chief executive, Miles Celic, said: "The UK-based legal services sector is the leading global centre for the provision of international legal services and dispute resolution."