Funding chiefs have challenged Ken Livingstone to a face-to-face session to justify his attempt to take control of college funding in London.
The Learning and Skills Council is fighting its corner after the Mayor revealed his ambition to take over the pound;1.4 billion budget.
In a consultation paper on the future of post-16 education and training in London, Mr Livingstone said: "The LSC, as currently set up, is unaccountable to Londoners and has failed to deliver for either the unskilled or employers, despite spending around pound;1bn a year."
David Hughes, the LSC's regional director for London, who plans to meet the Mayor in the next two weeks, said: "He has made this bald and bland statement and I want to ask him exactly what he thinks we are failing at.
"It is about how we are addressing our priorities and how we are going to spend all that money.
"We are saying we are doing a good job in London and have plans in train to make things better. Whether other people are convinced by that remains to be seen.
"It is difficult to see what the benefits are by going over to the Mayor.
There is a changing tide of people coming over to our position on that."
In a submission to John Prescott, the deputy prime minister, the LSC argues: "Having separate systems for London and the rest of the country will confuse learners and employers, a distraction we need to avoid."
The debate about the future of FE flows from Mr Prescott's announcement last year that he is looking at ways to shift powers away from Whitehall to the Mayor and the Greater London Authority.
He has launched a consultation exercise, to close on February 22, on the handover of responsibility for housing, planning and waste management as well as learning and skills.
Mr Livingstone wants the five local learning and skills councils in London to be merged and made accountable to him.
The LSC says it in favour of a greater role for the Mayor - as long as it retains control.
The LSC has argued that its successes in London include an81 per cent staying-on rate at 16, compared with 79 per cent nationally.
Targets for apprenticeships and for literacy, numeracy and language qualifications have been exceeded.
The report added: "The LSC is delivering and is changing now to deliver more. We would urge the Government not to damage this progress, to support us by endorsing our transformation agenda, not undermining it."
The LSC says the Mayor is mistaken in excluding school sixth forms from his plans and says the switch would have to wait for up to 30 months as legislation worked its way through Parliament.
Mr Hughes conceded that losing control in London could have knock-on effects for the LSC elsewhere.
He said: "If you take out one of the nine regions, and the biggest region at that, you start to question what is going to happen nationally. It is a question we haven't had any answers to."
The Mayor's officials believe London has different skills requirements to the rest of the country, with an economy increasingly requiring the workforce to be trained at level 3 (A-level equivalent) and level 4 (degree-equivalent) in vocational skills.
It is also confident that its links with businesses in the capital put it in a better position to meet industry's training requirements, with skills seen as crucially important to the Mayor's responsibility for economic development.
The Association of Colleges backs the LSC, saying the Mayor's plans have "profound implications" for colleges, schools and training organisations.
Natfhe, the lecturers' union, supports the Mayor's bid, arguing he would be more democratically accountable.