Cabinet member Peter Hain has welcomed donations to the Labour Party from financiers, despite union anger.
Peter Hain said all donations were welcomed
The donations from investors behind private equity funds are expected to be included in the Electoral Commission's quarterly publication this week.
The GMB union calls the funds "asset strippers," and wants the party's national executive to investigate.
However, Mr Hain said: "I think that it is right that we accept donations from people who want to contribute."
The GMB has been campaigning against private equity funds after firms, including the AA and Birds Eye, suffered job losses following takeovers.
General secretary Paul Kenny said: "Only in the last few weeks has the GMB campaigning put names and faces to the multi-millionaire elite who run the private equity industry and made clear what they do.
"Until that time most people in the Labour party will not have been clear about where this money was coming from.
"Maybe it is now time for the NEC to look into the background of where this money is coming from."
Mr Hain, Northern Ireland Secretary and a candidate for Labour's deputy leadership, said: "As far as the private equity schemes are concerned there is a concern, and the GMB union, for example, has raised this, about the way assets are being stripped.
Good and bad
"On the other hand private equity funds provide a very good vehicle for start-ups, for rescue operations and for investment to grow so we have got to make sure we distinguish the good from the bad.
"I think that it is right that we accept donations from people who want to contribute to the Labour Party and want to keep us in power.
"I don't think we should get into the business of saying all private donations are bad, all rich people shouldn't be contributing to the party - we want people to contribute to the party."
Media reports said investors Nigel Doughty, Sir Ronald Cohen and Jonathan Aisbitt each donated £250,000 during the final quarter of 2006.
A Labour Party spokesman said tonight: "All donations given to the Labour Party fully comply with guidelines laid down by the Electoral Commission who publish them regularly on their website.
"Nigel Doughty, Sir Ronald Cohen and Jon Aisbitt are all long-standing supporters of and regular donors to the Labour Party.
"The Labour Party receives support from many individuals and organisations that share our values of economic prosperity coupled with social justice and we welcome all their contributions."
'Lurch to the left'
Shadow Chancellor George Osborne defended the private equity industry as a success and suggested that Chancellor Gordon Brown was failing to confront a lurch to the left among the candidates for the Labour deputy leadership.
"Gordon Brown has stayed completely silent. You've not heard him come out and criticise these candidates for saying these things," he said on Sky's Sunday Live.
"You've not heard him come out and make the case, for example, for private equity, or indeed make the case for the current relationship with the trade unions rather than an enhanced one, and I think that's quite striking."
He said this was in contrast to Tony Blair a decade ago. "He...never hesitated to make the case to the Labour party that they should stay on the centre ground whereas Gordon Brown seems to lack the political courage to stand up to his colleagues in the Cabinet and say, look, the Labour party should not lurch to the left".