RTE's 'Operation Transformation' GP Dr Ciara Kelly said she can't afford to give free care to under-sixes.
Dr Kelly, a GP in Greystones in Co Wicklow, warned she could not provide a level of safe service that is necessary on €7 or €8 a month per patient, giving them 24-hour care.
"I passionately care about my patients but we cannot provide a service on a shoestring. Ultimately patient care will suffer," she warned.
Dr Kelly was among several hundred angry GPs who attended a meeting in Dublin last night, in protest at the "threat of extinction" to general practice as she told how her income was down 46pc.
She said she did not see any of her colleagues agreeing to sign up to the free care for under-sixes contract on offer, saying her private patients are subsidising her medical card patients.
She said €10 a month was not an economically viable fee to care for someone 24 hours a day. Her practice had to cut out much of the pro bono work such as the taking of free blood tests because they cannot afford it any more.
The National Association of General Practitioners, which organised last night's Dublin meeting and several others around the country, said more than 100 GP practices are at risk of shutdown and others face "imminent financial ruin".
Patients will end up losing out with less surgeries able to provide same-day appointments or callouts due to fees being slashed by €160m since 2010.
Stephen Murphy, a south Dublin GP, said GPs along the western seaboard, dependent on medical-card patients, face "insolvency" in many cases.
"The anger at the meetings around the country is extraordinary," he added.
Ray Walley, GP spokesman for doctors' union the Irish Medical Organisation, revealed they have again written to Junior Health Minister Alex White saying they will not accept an invitation to talks on the under-six contract unless they include discussions on fees.
The Government said it cannot discuss fees due to competition law. It means the promise of free GP care for under-sixes by the summer will not be met.
The meeting was told that young GPs are emigrating. Dr Aifric Ryan, employed in Johnstown, Co Meath, said she and her family are Australia bound.
"I have two small children to support. In the last nine months, I have become more and more despondent and cannot ever see me having a viable practice here," she said.
Dr Murphy told the meeting that GPs say many are working on average 70 hours a week just to keep their heads above water.
The strangest aspect of the Government's desire to reform primary care is that it is the only part of the system that is actually working efficiently.
Ironically, it is the one that has no waiting lists, and provides value for money.
It also consistently delivers the highest satisfaction rates.
However, while these resources have been plundered, the cost of staff, overheads and practice have not come down and unfortunately it is the most vulnerable members of society who will suffer, he added.
Health Minister James Reilly and Junior Minister White appealed to doctors to enter discussions on the contract. Both declined an invitation to the meeting of GPs last night.