Company bosses are urging the new government to publish a detailed list of Brexit priorities immediately after next month's General Election.
The new administration should be "upfront" as soon as possible to help industry prepare for leaving the EU, said the Institute of Directors.
Political parties should prepare documents spelling out their preferred outcome of the Brexit talks, the IoD said, adding there should be a "smooth transition" between membership of the EU customs union and a new agreement.
Allie Renison, head of EU and trade policy at the IoD, said: "These negotiations are not like any normal trade agreement.
"The scope for disruption is significant, so it would be better if the next government was as upfront as possible about their vision of Brexit.
"The EU has been clear about how it sees the process panning out, so after the election whoever is in Number 10 should quickly produce their own detailed objectives.
"We believe there is enough common ground, and good will, on both sides for the talks to be constructive, but more emphasis needs to be placed on the desired shape of our future relationship, rather than just reiterating red lines.
"The sooner after the election the government can spell out their priorities, the easier it will be for companies to plan."
O ne practical step would be to create a Brexit "voucher scheme" or tax relief expansion to help firms potentially at risk, she added.