The British government is facing possible defeat in the House of Lords as peers push for guarantees over the rights of EU nationals living in the UK after Brexit.
Shadow Brexit minister Baroness Hayter of Kentish Town warned against EU nationals being used as "bargaining chips" in negotiations to quit the EU.
Lady Hayter said the concerns of EU nationals here and British expats living in Europe shouldn't be "traded against each other".
Opening debate on the Brexit Bill in a crowded chamber, she said the Government should remove the uncertainty now.
"These people need to know now - not in two years' time or even 12 months' time.
They simply can't put their lives on hold," Lady Hayter said.
Home Secretary Amber Rudd has written to every peer urging them not to back the Opposition amendment to the legislation.
The European Union (Notification of Withdrawal) Bill has passed unamended through the Commons with big majorities.
Any changes to the legislation in the Lords would mean it would have to go back before MPs putting at risk Theresa May's timetable for triggering Article 50 and beginning Brexit talks by the end of this month.
Labour's amendment to the Bill, tabled with Liberal Democrat and crossbench support, calls for ministers within three months of triggering Article 50 to bring forward proposals ensuring the rights of EU citizens living here continue post-Brexit.
Lady Hayter said three million EU nationals were being used as "negotiating capital" by the Home Office and raised concerns about Britons living abroad.
"These two groups of people should not be traded against each other," she said. It was in the "gift" of the UK Government to decide how to treat people resident here.
"We don't accept, contrary to the letter sent yesterday by the Home Secretary, that this is a matter of our negotiations with the EU. This is a matter for the UK."
Lady Hayter warned about the impact on UK industries, the health and social care sectory, if the uncertainty continued.
She said the lives of EU national living in the UK were "too precious to be used as bargaining chips".