PARIS (Reuters) -French unions and employers negotiating changes to a 2023 pension reform are set to hold last-ditch talks next week, even as at least one major participant was not sure if it would join.

Prime Minister Francois Bayrou had agreed earlier this year to reopen the subject of pensions for talks between unions and employers as he aimed to win support from Socialists to survive no-confidence votes introduced by other opposition parties eager to topple him.

But months of talks ended on Tuesday without an agreement, and another "last chance" meeting has been set for June 23.

Patrick Martin, president of Medef, which represents employers, said in an interview with France 2 that the group may not participate, saying: "We were not the ones who asked for the reform to be reexamined."

Labour minister, Astrid Panosyan-Bouvet, told Franceinfo some progress had been made though a larger agreement remained elusive.

"We must continue because the way forward is possible," she said.

Unions want to roll back an unpopular 2023 reform that gradually raises the retirement age from 62 to 64, but employers are concerned doing so would require more payroll contributions.

Bayrou, a long-time debt hawk, has said all options were on the table as long as any modifications ensure a pensions funding gap is plugged by the end of the decade.

France's pensions system was close to balanced last year but is expected to show a deficit of 0.2% of GDP by the end of the decade and 1.4% by 2070 even with the 2023 reform, according to the national pension advisory's annual report.

French pension spending is among the highest in the world at 14% of GDP last year, with two-thirds paid for by current workers and employers' payroll contributions.

The rest is financed by hefty taxes and costly state transfers, with virtually no role for private pension funds common elsewhere in developed countries.

According to an Elabe poll for BFM TV, 70% of French people believe the current system is not financially sound, yet 63% oppose raising the retirement age, which some economists say is the most effective way of propping up the system's finances.