Some doctors providing out-of-hours care are being replaced with less qualified nurses and other workers, according to a poll.
A survey of 50 primary care organisations found that 19 had already cut the number of doctors they employed out of hours, replacing them with cheaper staff.
A further 10 were reviewing their emergency cover with a view to reducing the number of GPs they had, the survey for Pulse magazine said.
Some organisations had reduced the number of GPs on call by as much as 50%.
Last month, an influential group of MPs condemned Government preparations for the out-of-hours service as "shambolic".
The handover of care from doctors to primary care trusts in 2004 was riddled with flaws, the House of Commons Public Accounts Committee (PAC) said.
It said although the service was now starting to improve, the performance of trusts against key targets was "still not good enough".
Before 2004, GPs provided out-of-hours patient care - defined as between 6.30pm and 8am on weekdays and 24 hours at weekends and bank holidays.
But a new GP contract allowed them to opt out of providing it, with the responsibility passing to Primary Care Trusts (PCTs).
A Department of Health spokesman said: "Most patients are benefiting from improvements in out-of-hours services thanks to the new arrangements."
