Practices reported that they had dropped services such as travel clinics and stopped carrying out work including completing forms to support insurance claims or passport applications, according to the survey by GPonline's sister website Medeconomics.
GPs and practice managers also reported having stopped taking part in firearms licensing applications, despite a recent update to GPC advice warning that practices were legally obliged to 'engage in the process'.
Others reported dropping enhanced services to provide support for nursing homes or minor surgery, according to the poll of 306 GPs and practice managers.
The findings suggest that practices are struggling to find time to carry out work beyond core services that has long been an important source of additional funding. Eight out of 10 GPs now say their workload is unmanageable, according to a recent BMA poll of more than 5,000 doctors.
GPonline reported earlier this year that one in three GP practices had dropped unfunded work over the previous 12 months.
The Medeconomics poll found that more than half of GP practices say private fees are an important part of their practice income. GPC leaders say that around 5% of practices' income comes from this source.
But 34% of GPs who took part in the poll said their income from private fees had declined over the past 12 months, while just 19% said it had risen.
Practices that planned to drive up non-NHS income over the coming year said they would tighten up on charging for services that are outside of core work but have previously been delivered for free. Others said they would raise fees charged to third parties such as solicitors and lawyers, and refuse to complete forms without upfront payment.
GP private fees
GPC practice finance subcommittee chair Dr Ian Hume told GPonline: 'We are hearing and seeing that practices are making decisions to restrict the amount of private work they do and reviewing policies for what they charge, to make sure they are charging for services they haven't in past.
'They are having to make business decisions - the overriding priority is how they cope with workload.'
Dr Hume said that practices earn about 5% of their income on average from private fees. Many were struggling because of heavy workload and uncertainty over income, he warned.
'What we are seeing is the effects of reductions of MPIG, the impact of PMS reviews and practices reverting to GMS contracts, albeit with transitional funding offers,' said Dr Hume. CCGs were also altering their commissioning processes and reviewing areas like enhanced services funding as part of the shift to working at scale, he added.