GPs in Cardiff are claiming that a company due to co-ordinate out-of-hours health cover lacks relevant experience.
Out of hours doctors cover will be provided by Clinical Solutions UK
More than 80 family doctors attended a heated meeting, demanding more information about how the company, Clinical Solutions UK, will operate.
However, Cardiff Local Health Board, which awarded the out-of-hours contract, said the company would provide high quality care and had valid experience.
The board added that patients should not be worried about the level of care - however, the GPs maintain there are still unanswered questions.
The new out-of-hours arrangements come into force on 30 September, and are the result of responsibility for providing out-of-hours services passing from GPs to the health board.
GPs in Cardiff have been providing such cover through two organisations, Cadoc, a local GP co-operative running for eight years, and Primecare, a commercial organisation.
Cadoc had applied to the local health board to continue running the out-of-hours care, but its bid was rejected in favour of Clinical Solutions.
Members of Cadoc said they were unhappy no details of how Clinical Solutions would run the service had been released yet.
Alun Jones, director of Cadoc and a Cardiff GP, said: "We have been trying to ascertain a model of care which will address the real needs of the city, but there has been no adequate explanation how the service is going to be delivered.
"My worries as a patient would be what care would I get out-of hours," he added.
About 80 GPs attended the meeting hosted by the health board and Clinical Solutions on Tuesday.
They were hoping the company would reveal more about its plans, but say they were disappointed that it did not.
Sian Richards, the health board's chief executive, said there would be a public awareness campaign in early September "to ensure that all potential Cardiff residents will know how to access the new service".
She said providing information on the detailed changes beforehand "would be premature as it could give rise to confusion".
She also said Clinical Solutions had "extensive experience" in the UK, and internationally, and had provided services for NHS Direct in Wales and England, NHS24 in Scotland, and 43 NHS walk-in centres in England.
"The company has a very experienced team of clinicians with a proven track record in the out-of-hours setting, at a primary care level, and in working well with NHS bodies at both local and strategic levels," she said.
"Throughout the process we were extremely impressed by the calibre of the Clinical Solutions clinical team and the service they offered."
She said staff with local knowledge would be recruited by the firm.
"I can understand that the current providers of out-of-hours care are disappointed not to be selected but the decision has been made on a range of strict criteria, and we are confident that patients will receive a high quality service," she added.
Meanwhile Andrew Dearden, chairman of the Welsh GP committee of the British Medical Association said: "People do worry about change especially moving from one organisation to another or one structure to another and in this case from one provider to another.
"I think it's a little early yet to say whether we're in a crisis situation, whether it was a bad decision - we'll have to wait and see what the organisation does," he added.