The risk of a no-deal Brexit is turning into a "full-blown economic crisis", the aerospace trade body has warned.
ADS Group said it was now able to track "the very real economic damage being caused" by the continuing uncertainty over the UK's exit from the EU.
Its warning comes as insurance trade body, the ABI, said a no-deal Brexit "would be a be an unforgivable act of economic and social self-harm".
The UK is due to leave the EU on 29 March, but no deal is yet in place.
Prime Minister Theresa May is facing growing pressure to delay Brexit if no deal is agreed by then.
ADS, the aerospace and defence trade group, represents some of the largest companies operating in the UK, including Airbus, Boeing and BAE Systems.
Chief executive Paul Everitt said its members needed a "firm transition period and negotiations on the UK's future relationship with the European Union commenced at the earliest opportunity".
His comments come amid growing anger among many business groups over the continuing uncertainty.
Huw Evans, director general of the Association of British Insurers, is expected to suggest at a dinner on Monday evening that "as a last resort" Brexit should be subject to a short delay if no deal is the only alternative.
Mr Evans will say that any future arrangement with the EU that required the UK to comply with rules over which it had no say could be "weaponised by those in the EU that want to… damage the UK".
On Sunday, Mrs May announced that MPs will be able to have a fresh vote on the Brexit deal by 12 March, prompting expressions of dismay by several business groups.
CBI deputy director general Josh Hardie described it as "the latest signal to businesses that no-deal is hurtling closer".
"It must be averted. Every day without a deal means less investment and fewer jobs created," he said.
British Chambers of Commerce director general Dr Adam Marshall said: "Delaying the vote until just two weeks before the UK's planned departure from the EU raises serious concerns about the timeline of the parliamentary process, and whether there is sufficient window to reach an agreement and pass the necessary legislation to avoid a no-deal exit."
And the Institute of Directors' interim director general, Edwin Morgan, said: "There is too much at stake to run down the clock and risk an accidental no-deal. We sincerely hope this is the last and final date change."
He added: "Businesses have lost all faith in the political process and as those first in the firing line of no-deal, they deserve to know more."