Labour leadership contender Michael Meacher has called on BP shareholders to try to block a multi-million pound payoff for departing boss Lord Browne.
Lord Browne is leaving in July
Mr Meacher, a former government minister, estimates the BP boss could get up to £72m when he leaves in July, although it is likely to be less.
Lord Browne is expected to gain a £5.3m cash package, up to £21m of extra BP shares, and a pension worth £21.7m.
The UK oil giant said it took note of shareholder opinion.
Mr Meacher's comments come ahead of BP's annual general meeting on Thursday.
Mr Meacher wishes to succeed Tony Blair
Shareholders are due to vote on executives' pay at the meeting, including Lord Browne's leaving package, yet BP stressed that the vote would not be binding.
"I call on BP shareholders to reject this grotesque pay-off," said Mr Meacher.
"We need to end the situation where city bosses set each other's rewards.
"The remuneration committees that decide on chief executive pay should include representatives from the shop floor, to inject a sense of reality."
Mr Meacher's comments come after pensions pressure group Pensions Investment Research Consultancy criticised Lord Browne's expected payoff, saying it had "significant concerns".
BP reported last month that Lord Browne's pay packet had shrunk for the second year in a row to £4.57m in 2006, down 28% from 2005.
The oil firm announced in January that Lord Browne would retire in July, 18 months ahead of his original departure date at the end of 2008.
BP has suffered problems in recent years including oil spills in Alaska and an explosion at one of the firm's US refineries in 2005 in which 15 people died.
Lord Browne has been with BP for 40 years, and led the firm for 12.