GP leaders warned that cost cutting and competitive tendering could force GP-led out-of-hours providers out of business.
Data obtained under the Freedom of Information Act show 20 PCTs forecast savings of around £4 million in total on out-of-hours in 2010/11 compared with 2009/10 spending.
Many PCTs reduced costs by renegotiating or retendering out-of-hours contracts. One of the largest savings was made by NHS North Lancashire, which saved £487,000 through retendering part of its service. NHS Oxfordshire saved £411,427 by sub-contract renegotiation and retendering.
Other PCTs made management savings or spent less because of changes to accounting processes or paying start-up costs in 2009/10.
Some PCTs that cut spending said their out-of-hours service would remain unchanged, but the GPC warned cutting costs could hit patient safety.
GPC deputy chairman Dr Richard Vautrey said increasing pressure on out-of-hours GPs to see more patients faster would leave doctors tired and more prone to mistakes.
He said: 'If you pare a service down and reduce funding to such a level you may put patients at higher risk. The cheaper the service is, the less patients are satisfied.'
Dr Fay Wilson, chairwoman of Birmingham out-of-hours co-op BADGER, warned competitive tendering could freeze GP-led organisations out of providing services. 'My anxiety is that only big organisations with international backing can provide the service at a knock-down price,' she said.
Cutting out-of-hours spending could also increase hospital admissions and ambulance journeys. 'It looks as if out-of-hours is cheaper, but if you are spending it elsewhere then it is a false economy,' Dr Wilson said.
She added some PCTs may have been paying 'over the odds' if they used non GP-led services, and could cut costs safely.
NHS Tameside and Glossop forecast it would reduce funding for out-of-hours because global sum increases meant GP out-of-hours opt-out payments had increased.
Dr Wilson said the amount PCTs spend on out-of-hours should not be linked to the amount GPs pay to opt out.
A total of 78 PCTs responded to GP's request for information. Across all 78 PCTs, out-of-hours spending rose just £3.6 million in total for 2010/11.