GDP would fall by 4% if all non-Brits stopped working for 24 hours, according to the New Economics Foundation.
The UK economy would take a £328m hit if all migrant workers downed tools for a day, according to new research.
GDP would fall by 4% if all non-Brits stopped working for 24 hours, the New Economics Foundation (NEF) said.
It said institutions like the NHS, which employ large numbers of immigrant workers, "would be unable to function".
The research comes as thousands of people prepare to take part in 1 Day Without Us, a pro-migrant "day of action" showing how much immigrants contribute to the country.
At about the same time, MPs will debate a petition against US President Donald Trump's planned state visit to the UK.
A demonstration is planned outside Parliament over Mr Trump's attempt to ban travellers from seven majority Muslim countries.
NEF chief executive Marc Stears said: "Britain has a long and proud tradition of openness to people from overseas and our research conclusively shows that migrants have more than repaid for the welcome they have received.
"Our future as a country depends on the economic, cultural and social contribution that migrants make.
"As countries all around the world succumb to the siren call of populism, we need to remember that contribution and to celebrate it."
According to NEF, migrant workers in the UK make up 10.9% of the total workforce.
Citing Migration Observatory figures, it claims this percentage increases dramatically in some jobs, including cleaning and household staff (31%), food preparation and hospitality workers (30%) and health professionals (26%).
Rachel Taylor-Beales, one of the organisers of 1 Day Without Us, said the event was "about celebrating the many diverse ways in which migrants have contributed to Britain".
SOURCE: Sky News
