The board of the Midcounties Co-operative, which operates gas and electricity supplier Co-operative Energy as well as Co-op-branded food stores and other businesses, voted against proposals being devised by Lord Myners.
But they were accused of grandstanding by a source close to the Co-op while Lord Myners, a former City minister, said the vote looked "premature" given that his report would not be complete until the end of this month.
Reform plans include a move to abolish the wider group's vast 21-member board, splitting it into two with a plc-style panel responsible for commercial decisions and representatives from its traditional membership sitting on a separate body. The Co-op group board has already agreed to this but the shake-up still needs to be agreed by members.
The Co-op recently delayed the publication of annual results, expected to reveal losses of £2 billion.
A source close to the Co-op played down the impact of the "meaningless" Midcounties move. "It would appear that taking a vote on a report that is not yet complete is a political statement," the source added.