Almost three-quarters of GP practices will reportedly open as normal on Thursday when doctors take industrial action for the first time in almost 40 years.
A poll by Pulse magazine said only a quarter of practices across the UK have notified their primary care organisation that they will be taking part in the strike.
Across 20 primary care organisations, 281 out of 1,265 practices have so far notified NHS managers they are taking action. Up to 100,000 doctors who are members of the British Medical Association (BMA) could be on strike in protest at the Government's pension reforms.
Last week Pulse reported that hundreds of GP practices were notified that they could be hit with compensation claims from NHS managers if they are found to be in breach of contract.
It said that PCT clusters in London wrote to all 1,331 practices in the capital, saying: "The local NHS may decide to withhold certain payments due to a contract holder by way of compensation for any breach, should it occur. In addition, formal contract breach notices would be issued."
The Royal College of Midwives has advised its members not to do anything to "undermine" the industrial action. It urged members to "work as normal" on Thursday.
According to Health Secretary Andrew Lansley, the planned strike could see up to 30,000 operations cancelled, 58,000 diagnostic tests postponed and 200,000 outpatient appointments rescheduled. Mr Lansley also said up to 1.25 million GP appointments would be pushed into the days and weeks following the action.
The BMA announced the strike last month after it accused ministers of pressing ahead with "totally unjustified" increases to pension contributions and a later retirement age for doctors even though a deal on pensions was agreed four years ago.
All non-urgent work will be postponed, the BMA said, adding that although the action will be disruptive, doctors will ensure patient safety is protected.
Doctors will see anyone who is ill, or who believes they are ill, on the day of action but will not do paperwork. Local NHS managers have urged patients to only use services if there is an urgent need. Most doctors will be taking industrial action for the first time, with the last dispute almost 40 years ago.