If Labour policies do not change key party figures should quit, the general secretary of the UK's largest private sector trade union has warned.
Derek Simpson said Amicus would retain links to Labour
Derek Simpson, leader of Amicus, one of the biggest affiliates to the Labour Party, said Labour was increasingly "out of step" with millions of people.
He warned that support for the party was waning.
Union members were increasingly asking why Amicus was still giving Labour more than £1m a year, he said.
Mr Simpson said it almost "stuck in the throat" to suggest that Tony Blair should stand down if he was not prepared to change direction.
The former shop steward told BBC Radio 4's Today programme it was the policies that were wrong, not personalities.
He said: "The policies Tony Blair is following could lose Labour the next election, by just concentrating on those issues that we all acknowledge, the NHS investment and investment in education.
"These are obviously very important matters but this ignores the collapse of manufacturing business and pensions crisis, creating the perception that the government is doing not enough."
There are growing fears about the fall in the value of modern pensions, the decline of final salary schemes and proposals to increase the retirement age to 70.
Amicus is not about to break links with the party as it is one of the four big unions campaigning for a radical third term.
It represents more than a million professionals working in the health, manufacturing, science and finance sectors.