Tens of thousands of migrants and their supporters are staging their first day of action on Monday to highlight their contribution to the UK economy, alongside a thousand EU citizens demanding the right to remain in Britain after Brexit. A report from the New Economics Foundation estimates that if every migrant withdrew their labour for one day, it would cost the UK £328m – 4% of the country’s GDP. Migrant workers in the UK make up 10.9% of the total workforce, but according to the Migration Observatory, that number increases dramatically in certain key sectors. Some 31% of cleaning and household staff, 30% of food preparation and hospitality workers, and 26% of health professionals are foreign-born. Also participating in the campaign are approximately 1,000 EU citizens, who will descend on Westminster to lobby MPs over their fight for a guarantee of the right to remain in the country post-Brexit.They will assemble in a local church hall and at lunchtime head towards two allocated committee rooms in the House of Commons to lobby 50 MPs, who have agreed to meet them. Among them will be Labour’s Brexit spokesman, Keir Starmer, Labour MP Stephen Timms, who sits on the Brexit select committee, Tory MP Philip Davies, and the Green party leader Caroline Lucas. Universities, trade unions and art galleries including the Tate and Tate Modern are backing the day of action. The day is also being supported by national organisations, including the 3 Million organisation, New Europeans and UNISON. A number of businesses will close for the day to help make the argument that the UK would struggle to manage without the contribution of migrants, even for a day. At one o’clock, people supporting One Day Without Us are being asked to gather in public spaces and simultaneously link arms in a gesture of solidarity and appreciation of migrants. Westminster will also be the focus for some of the actions of the day. A “flag mob” is planned, with people being invited on social media to descend on parliament square carrying the flag of the country of their birth, to illustrate how many nationalities are represented in Britain. The action comes as a petition to rescind President Trump’s state visit to Britain is debated in Parliament following his travel ban. One of the organisers of the day, Matt Carr, said: “There’s never been a national day of action in support of migrants in this country before. Too often migrants are portrayed negatively in the UK and blamed for problems they didn’t cause. Today we celebrate the contributions that migrants make and reject the politics of division and hatred.” The Guardian view on EU citizens’ rights: compassionate diplomacy needed Editorial: Ending the uncertainty for EU nationals in the UK would be a smart strategic move and a just one. It might also help to give a debate that can blur into racism a much-needed new vocabulary of understanding Read more Dave Prentis, general secretary of UNISON, which represents workers in the public sector, including health workers and social workers, said that “unless ministers guarantee European workers the right to remain now, they risk losing thousands of well-trained health and care staff for ever”. He said it was not good enough to allow those health workers who are vital to the NHS to spend the next two years unable to plan their futures. British people living in Europe are also concerned for their futures, and are supporting Monday’s event. Jane Golding, co-founder of UK citizen support group Brits in Europe, who lives in Germany, said the UK should make a unilateral move now because it was the right thing to do. “Free movement has always worked both ways; just as large numbers of Brits have left the UK to live and work in other EU countries, so have EU citizens come to the UK in good faith to do the same. These are people with rights, and these rights cannot be withdrawn retrospectively.”