The GPC hit out at the 'huge workload implication' that draft NICE guidance would have on the resources of already stretched practices.
NICE denied the guidance, which aims to tackle rising rates of diabetes, would strain workload.
Under the proposal, GPs must use a validated risk-assessment tool to identify all high-risk patients aged 25 and over. Practices would also offer self-assessment surveys to all non-pregnant adults over 25.
All those identified as high-risk should then be invited for a blood test to confirm risk or detect undiagnosed diabetes. The plan would also see GPs offer blood tests to all adults of south Asian or Chinese descent aged over 25 and with a BMI above 23kg/m2.
GPC prescribing lead Dr Bill Beeby told GP: 'At the sharp end there will be a substantial amount of work involved. We may not have the capacity or resources. We might be able to offer this opportunistically, but a systematic screening programme needs very careful consideration.'
A NICE spokesman said: 'The practice risk score uses routinely collected data that is included in all medical records. This is very little work - though it helps if records are up to date.'
NICE admitted there was 'very limited evidence' for risk assessment among adults aged 18 to 39 and that risk scores for this group should be used with caution.
Dr Beeby said: 'If the evidence is limited, why recommend it?'
Professor Mike Kelly of NICE said the guidance would help identify 'potentially thousands of people' at risk of developing type-2 diabetes and set out interventions to cut risk.
It comes as a University of Leicester study found that south Asians with a BMI of 23 to 28 were at similar risk of diabetes and cardiovascular disease as white Europeans with a BMI of 30kg/m2.
A consultation on the NICE proposals will run until 9 January.