Five major UK business bodies have come together to call for continued access to the European single market until a final Brexit deal is made with the EU.
In a letter to Business Secretary Greg Clark, they also ask the government to "put the economy first".
The letter is from the British Chambers of Commerce, Confederation of British Industry, EEF, Federation of Small Businesses and Institute of Directors.
Formal Brexit negotiations between the EU and the UK begin on Monday.
The signatories say the "economic benefits" of the European Union single market, which allows free movement of goods, services, capital and people, and the customs union, which enables tariff-free trading within the EU, should be maintained until a final settlement between the UK and the EU is "agreed and implemented".
They have also called for a final trade deal that will allow tariff-free goods to be traded between the UK and the EU.
In addition, they want that deal to include "minimal customs formalities", mutual recognition of standards and regulation, and a "flexible system" for the movement of labour and skills.
"We have come together to urge the government to put the economy first as it prepares to start formal negotiations," says the letter to Mr Clark.
"This is a deal that when finally agreed will matter fundamentally for the UK economy, for UK companies and for citizens of the UK."
Monday's talks between Brexit Secretary David Davis and EU negotiator Michel Barnier follow preliminary negotiations in Brussels between officials.