Business leaders who employ around one million workers in the UK and EU will sign a letter this weekend, imploring both sides of the Brexit negotiations to get a move on.
A draft of the letter, seen by the BBC, urges negotiators to clarify the rights of UK and EU citizens working abroad by October.
It also calls for real progress towards future arrangements by the end of 2017.
The leaders said a deal was imperative to safeguard jobs and investment.
The letter was drawn up by trade group the CBI and circulated to top business leaders.
It is expected to draw more support than a UK government text that asked Britain's biggest businesses to endorse the government's approach to Brexit negotiations.
'Written for business'
There was widespread reluctance from FTSE 100 bosses to support a strategy that many thought lacked clarity.
One FTSE 100 chairman told the BBC: "I think this is a much better letter than the one the government tried to circulate - it's written for business by business."
However, other business leaders contacted by the BBC - while broadly supportive - were cautious about the impact that a letter from business leaders would have.
"I'm still not sure there is much value in letters like this," one told me.
After an election campaign that saw the Conservative Party distance itself from big business, bosses have reported a thawing in relations with government.
Some of the UK's top business leaders will gather tonight at the government retreat in Chevening to discuss the process of withdrawal from the EU and future trading relationships.
I'm told that neither the CBI, who organised this collective letter, nor other business lobbying groups are invited.
Draft text of the CBI's letter:
"We represent businesses of all sizes, sectors and regions of the UK and employ nearly one million people in the UK and EU.
"We are committed to helping secure a successful new economic partnership between the UK and the EU, based on the principles of barrier-free trade. We welcome the strengthened collaboration between business and government to achieve this. This must now lead to progress.
"Our businesses need to make decisions now about investment and employment that will affect economic growth and jobs in the future. Continuing uncertainty will adversely affect communities, employees, firms and our nations in the future.
"Businesses across the EU and UK are clear: being able to plan for a transition of up to three years that avoids a cliff edge is critical for our collective prosperity.
"We are therefore writing to urge both sides to be pragmatic and determined to move to the next stage of the negotiations. Until transitional arrangements can be agreed and trade discussed the risk of 'no deal' remains real and has to be planned for, with inevitable consequences for jobs and growth on both sides."
"We ask you to ensure that substantive progress is achieved during the upcoming negotiations. Only this will give certainty on the rights of EU and UK citizens working abroad and enable discussion of transitional arrangements in October and trade, by the end of the year.
"Our shared interests vastly outweigh our differences, and we stand ready to help in any way we can to secure a successful outcome for the people and communities of the UK and the EU."