Health secretary Alan Johnson has written to every GP in England asking them to see patients at evenings and weekends in a bid to reduce the amount of time lost in sickness absence.
Johnson hopes to persuade the average-sized practice to open three extra hours a week so employees can obtain appointments outside work hours.
Doctors’ body the British Medical Association remains bitterly opposed to the plans, saying GPs should get more money to open later.
But the government has insisted it will impose longer hours if an agreement cannot be reached.
Health minister Ben Bradshaw said: “I think it stems on our part from a concern that the current leadership of the BMA doesn’t really speak for the profession at large.
“They’ve misrepresented the negotiations and they’ve misrepresented the offer that the government is making.”
In August employers’ group the CBI called for changes to doctors’ hours after an official report showed they were working up to seven hours per week less than 15 years ago.
The CBI said that millions of days of work were lost each year because of inflexible GP hours.