Economy would lose £328m if non-Brits stopped working for a day - research
The UK economy would take a £328 million hit if all migrant workers downed tools for a single day, new research suggests
The nation's GDP would fall 4% if all non-Brits stopped working for 24 hours, according to the research by the New Economics Foundation (NEF).
It also said institutions like the NHS, which employ large numbers of immigrant workers, "would be unable to function".
It comes as thousands of people are due to take part in 1 Day Without Us, a pro-migrant "day of action" showing how much immigrants contribute to the country.
Monday will also see MPs debate a 1.85 million-signature petition against US President Donald Trump's planned state visit to the UK.
It will be followed by a demonstration planned for outside Parliament over his attempt to ban travellers from seven Muslim countries entering the US.
Marc Stears, the NEF chief executive, 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."
Events are planned for 1 Day Without Us in England, Scotland, Wales and Northern Ireland, at university campuses, town centres and private businesses.
According to NEF, migrant workers in the UK make up 10.9% of the total workforce. But citing Migration Observatory figures, it said that number increases dramatically in some jobs, including cleaning and household staff (31%), food preparation and hospitality workers (30%) and health professionals (26%).
Uta Rosenbrock, a German citizen who owns a jewellery shop in Edinburgh, said: "I have, over the years, employed women from Australia, Canada, Czech Republic, Slovakia, Poland, Spain and of course Scotland.
"I have taken pride in being part of a vibrant, multicultural community in Edinburgh. Never have I questioned my right to be here, all my adult and working life has been in Scotland.
"Now, suddenly, all of that is in question. I am closing my shop on February 20 so the community see what they stand to lose if we all leave."
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".
She added: "These extend well beyond the economy. But it is striking to see just how much migrants do add to economic output in a single day and what this country would lose if they weren't here."