"The committee president has decided to ban wine during the finance committee meals without informing anyone," Daniel Sormani, a representative of the populist Geneva Citizens' Movement wrote in a letter to his colleagues cited by the Tribune de Geneve (TdG).
The decision "shocked the vast majority of the committee", he said, demanding a reversal.
Committee president, Socialist Alberto Velasco, meanwhile, maintained the move was necessary, describing how insults began flying as the bottles on the table emptied.
The 15-member committee meets between 5.30pm and 10pm over a warm meal, until now accompanied by two bottles of wine.
While the quantities are modest, Velasco told TdG that half of the committee did not drink, so the remaining members each got a few glasses.
"We are dealing with large amounts of money," he said.
"By lowering the alcohol levels . . . we will be more deserving of the citizens' confidence".