Bristol City Council has blocked calls for an independent inquiry into its energy firm, Bristol Energy.
The council has invested £35m into Bristol Energy, set up in 2015, which has so far posted losses of £32.5m.
Labour mayor Marvin Rees said he has acted in its “best interests” by not revealing the full financial picture.
But at Tuesday’s meeting, opposition councillors responded by accusing the council of hiding behind a “cloak of commercial confidentiality”.
Opposition Conservative, Liberal Democrat and Green councillors put forward the motion calling for an independent inquiry at the extraordinary meeting but this was blocked by the Labour majority.
The mayor blamed the previous administration for creating the company, the local Democracy Reporting Service (LDRS) said.
He added: “They had the party and we’ve been left to cope with the hangover.”
Earlier this month, the city council announced it would be putting the firm up for sale, the LDRS said.
But Conservative group leader Mark Weston said it was time for the administration to accept Bristol Energy was a “dead weight” on council finances and it should be “released”.
“What we want is an inquiry,” he said.
“Let us investigate exactly what happened, when it happened, the funding that goes with it, because I fear we have a bombshell about to explode in this city’s finances that is going to cost us millions.”
Seconding the motion, Lib Dem group leader Gary Hopkins said it was obvious more than two years ago that Bristol Energy was in trouble and accused the mayor of a “cover up” once he realised the company was beyond rescue.
Mr Rees said councillors and the public would be able to ask questions about Bristol Energy’s finances at a cabinet meeting on Tuesday.