A new cross-party campaign is urging Theresa May and her European counterparts to give EU and UK nationals reassurances over their right to remain after Brexit.
The Write to Remain group, established by Open Britain and CommonGround, is encouraging people to send messages to the British prime minister.
The campaign's aim is to get May to make an "explicit commitment" to fair treatment for all of the 3.6 million EU citizens in the UK and to ask her European counterparts to do the same for Britons on the continent.
"EU citizens living in the UK are our friends, neighbours, and workmates. They might be your doctor or your child's teacher," said Frances O'Grady, the general secretary of the Trades Union Congress (TUC).
"It's immoral to keep them in limbo, and inhuman to treat them as bargaining chips.
"The public believes they deserve to stay, and Brits living on the continent need a guarantee they can stay too. So we call on the prime minister to do the right thing and sign a joint commitment to the right to remain."
The UK's vote to break away from Brussels on 23 June has left EU nationals in the country with uncertain futures, with May being accused of using them as "bargaining chips" in Brexit negotiations.
International Trade Secretary Liam Fox has described the EU citizens as one of the "main cards" in the government's negotiating arsenal.
But a joint statement from the Home Office, Cabinet Office and Foreign Office stated in July that the government expected that the legal status of EU nationals in the UK and Britons on the continent will be "properly protected".
The UK still has not formally begun the process to leave the EU. May has promised to trigger Article 50, the official mechanism to split from the political and economic bloc, by March 2017.
But her administration is currently facing a challenge in England's High Court, while MPs such as former Labour leader Ed Miliband call for parliament to have a say on the issue.