A poll carried out this winter by BMA Wales found that 57% of around 100 GPs who responded were involved in out-of-hours work.
Among GPs who did not work out-of-hours, exhaustion caused by the daily pressures of general practice was the most common reason - with 64.3% of respondents citing this as a factor.
More than a quarter of GPs (40.5%) said they simply 'don't want to' work out-of-hours, and 38.1% said rates of pay for the work were not attractive.
However, GPonline reported last year that three in five GPs had been forced to turn down work or reduce the number of sessions they work because of indemnity costs - and the BMA Wales poll confirmed this finding, with doctors citing fears of 'exceeding indemnity allowance' as a reason for turning down work.
Doctors also said they were put off out-of-hours work after experiencing 'frequent uncovered shifts' and doctors being substituted by other health professionals.
In total 81% of respondents to the poll who currently do not work out-of-hours said they 'would not consider' working for the service in the future.
Changes to the taxation status of doctors working out-of-hours shifts - following implementation of advice from HMRC - have also undermined benefits for doctors, BMA leaders have warned.
GPC Wales chair Dr Charlotte Jones said: 'These results aren’t surprising and confirm what we have known for some time. The pressures that GPs face day in, day out are leaving them exhausted. This exhaustion can ultimately lead to burnout and GPs leaving the profession early, further compounding the problem.
'The system as a whole is under a sustained amount of intense pressure, brought about by an increase in workload and inadequate resources due to years of underinvestment. This is a significant problem facing in-hours services but is particularly acute for out-of-hours services, meaning out-of-hours is viewed as an unattractive place for GPs – who despite everything continue to provide high quality services for their patients – to work.
'Changes to HMRC regulations and the way each health board is implementing the changes has led to GPs who do work out-of-hours feeling undervalued and not appreciated.'
Dr Jones called for 'true investment' in out-of-hours services to guarantee safe staffing and make the service an attractive place for GPs to work.
'If urgent action is not taken patient care will be impacted,' she warned. 'Services will continue to be inadequately staffed, and in some cases not staffed at all, which will lead to longer waiting times, reduced appointment availability and a need for patients to travel longer distances to access care. One of these issues alone would have an impact but together will inevitably add considerable pressure onto colleagues in practices, secondary care and the ambulance service.'