Mr Byers said the party must listen to the message from voters
Former cabinet minister Stephen Byers has added his voice to calls for Prime Minister Gordon Brown to stand down.
Mr Byers said Labour needed a leader who could win a general election "and not take us to a humiliating defeat - Gordon Brown is not that leader".
Mr Brown should stand down for the sake of people who needed a Labour government to protect their interests, he told a Progress think tank meeting.
But Mr Brown was applauded at a meeting of the Parliamentary Labour Party.
Former home secretary Charles Clarke has also called for Mr Brown to quit.
Mr Byers said: "Gordon Brown knows the real price that will be paid for a Labour defeat.
"For those people, families and communities who need a Labour government to protect and promote their interests, now is the time for Gordon Brown to stand down as Labour leader and prime minister."
He attacked party members who argued that Labour was "getting on with the job", saying "it fails to recognise the monumental scale of the electoral rejection that we had last Thursday".
"We need someone who can voice the concerns of the British people and who can identify with their needs, a leader who is decisive and not timid, who can inspire and take our country though these difficult times," he said.
At a meeting of the Parliamentary Labour Party earlier on Monday, the BBC understands there were calls for Mr Brown's resignation from Mr Clarke and MPs Fiona McTaggart, Tom Harris and Siobhan McDonagh.
But the Labour leader was applauded by most of the MPs as he made what he called "an argument for unity".
BBC political correspondent James Landale said they cheered and banged desks in support of Mr Brown.