Neil McEvoy seeks alliance to remove Labour in Cardiff council
Calls have been made for Plaid Cymru to form an alliance with other parties at next year's Cardiff election to remove Labour from power in the city.
Neil McEvoy, leader of the party's group on the city council, said co-operation with the Liberal Democrats, Greens and independents would result in a "clear majority".
The Lib Dems said they were "prepared to have a discussion" with Plaid.
But Labour said Mr McEvoy was "carving up our city behind closed doors".
Labour currently controls Cardiff council after winning 46 of the 75 seats at the 2012 council election but it lost two recent by-elections - Plasnewydd to the Lib Dems and Grangetown to Plaid.
Mr McEvoy, who is also AM for South Wales Central, said the by-elections were an example of Plaid and Lib Dem co-operation working.
He wants the parties to agree common policies including revoking the Local Development Plan, re-opening recycling centres and investing in youth services.
"It's about where best to focus resources in the city. There's no point in the opposition cutting each other's throats," he said.
"Cardiff has experienced the most disastrous mismanagement in its history over the last four years. Labour's defeats in Plasnewydd and now Grangetown show people want change."
"I would like to see an anti-blue and anti-red Tory alliance across the city made up of parties and independents willing to sign up to basic policies to deliver.
"We could win a clear majority. The only question would be who would be the biggest party.
"A coalition would be the logical conclusion."
Mr McEvoy said he was not advocating similar alliances in other council areas, saying he can only speak about the situation in Cardiff.
At the assembly last month, Plaid agreed to support the Labour government's budget in return for commitments to various Plaid priorities, a decision Mr McEvoy opposed.
The leader of the Lib Dem group on Cardiff council, Judith Woodman, said: "We're prepared to have a discussion but our policy is to stand candidates everywhere we possibly can to enable people to vote Lib Dem.
"It's not just for me to discuss it. We need the discussion and we'll then decide if it will work for the Lib Dems or not."
The Cardiff Green Party said it has had "informal discussions" with other parties but there were no "definitive agreements".
Its campaigns co-ordinator Anthony Slaughter said the party recognises "the growing need to work across traditional party lines".
A Cardiff Labour group spokesman said: "Neil claims to be a campaigner for transparency in politics, yet is happily carving up our city behind closed doors.
"It's bizarre that opposition parties are fielding candidates with no intention of actively seeking support."
The spokesman added that the public are "entitled to know" if Plaid and the Lib Dems co-operated in the recent by-elections and called for details of any discussions between the two parties to be published.