Labour MPs have been told they will be automatically reselected as candidates in their constituencies for the general election on 8 June.
Jeremy Corbyn had hoped to give party members a say in who was chosen, but has accepted there is insufficient time to do that before polling day.
However, one Labour MP has told Mr Corbyn there is still time for him to stand down as leader before the vote.
Labour will endorse the PM's call for a snap election in a Commons vote later.
Mr Corbyn welcomed the prime minister's election announcement on Tuesday, calling it a "chance to vote for a government that will put the interests of the majority first".
Shadow chancellor John McDonnell said Labour would support the vote in Parliament for an election, calling it "an opportunity for removing a Tory government and replacing it with a Labour government".
Setting out the party's manifesto ideas he said the government had a mandate for Brexit but not for the hard Brexit currently set out.
Labour wanted the government to negotiate with the EU for tariff-free access to the single market; managed and fair immigration; and to seek to maximise the benefits from the customs union, he said.
But he said the election had been called because the government saw "the economy is going to turn, we are seeing inflation increasing, wages stagnate and people in heavy debt. They also know our public services are in crisis, the NHS and schools..."
He said Labour wanted a pay ratio, from the top to bottom earners in a company. And it was "looking to the corporations and the rich to pay their share" in fair taxation to afford public services.
Labour MPs and peers met on Tuesday evening in the wake of the election announcement.
BBC political correspondent Chris Mason said Mr Corbyn had been met by only cool applause.
Afterwards, one MP was heard to say: "Go back to your constituencies and prepare for... the Guardian jobs page."
Earlier, in a video, John Woodcock, the Labour MP for Barrow-in-Furness, said there was still time for Mr Corbyn to stand down "rather than lead Labour to defeat".
In the Facebook video, Mr Woodcock, a long-standing critic of Mr Corbyn, said he was seeking re-election in his constituency, but could not endorse Mr Corbyn as the next prime minister.
The Labour leadership has insisted there is "a very positive mood" in the party and it looked forward to presenting "a real alternative" to the Conservatives.
Former Home Secretary Alan Johnson has said he will not be seeking re-election in the Hull West and Hessle seat he has represented since 1997.
And Tom Blenkinsop, who has been MP for Middlesbrough South and East Cleveland since 2010, said he would not be standing for re-election, citing "irreconcilable differences" with the party's leadership.