Junior doctors have been marching in London in protest at planned changes to their contracts in England.
Their union, the British Medical Association, says the plans will lead to a drop in junior doctors' salaries.
Health Secretary Jeremy Hunt has accused the BMA of misleading doctors and says the proposals would reduce their maximum weekly working hours.
The BMA rejected Mr Hunt's claim and said the rally in Westminster was a "wake-up call for ministers".
Thousands of junior doctors also staged rallies in Belfast and Nottingham.
Critics say the new contract involves pay cuts of up to 30%, with "normal hours" extended to include 07:00 to 22:00 every day except Sunday.
However Mr Hunt told BBC Radio 4's Today programme that the proposals would benefit doctors by reducing their maximum weekly working hours.
Mr Hunt said he wanted to remove financial penalties "that force hospitals to roster less at weekends" and was willing to negotiate over safeguards that will stop doctors from working too many hours.
"This is a good deal for doctors. We are reducing the maximum hours a doctor can be asked to work from 91 to 72 hours [a week]. We're stopping doctors being asked to work for five nights in a row."
Mr Hunt also called on the BMA to return to the negotiating table.
The BMA is demanding that the government withdraw its threat to impose the new contract in England from next year.
Scotland and Wales have both said they will maintain the old contract, while Northern Ireland has yet to decide.
Speaking to the BBC from the central London protest, junior doctor Animesh Singh said: "I have looked at the contract proposal with an accountant friend and looked at the kind of rotas I work.
"For me as an 11-year junior doctor I would see a 15% cut in my pay and that's someone who's looking after patients who come into casualty every day of my working life."
Before the rally in London, Dr Johann Malawana, chairman of the BMA junior doctors' committee said: "The truth is that the junior doctor contract is in no way a barrier to seven-day services, with the vast majority of junior doctors routinely providing care to patients 24/7."
Dr Dagan Lonsdale, a specialist registrar working in intensive care medicine, said: "If I am one of the doctors who loses out in this new contract, then again for my wife and I it becomes financially unviable for us to remain as doctors."
By Hugh Pym, BBC health editor
There is a sense that Jeremy Hunt's patience is wearing a little thin. His latest interview is in effect an attempt to sidestep the BMA and appeal to the wider body of junior doctors in England.
But the BMA's response is that the thousands of doctors protesting in London, Belfast and Nottingham demonstrate the strength of feeling and unity behind the campaign against the controversial new contract.
The question is how ministers will respond to the weekend's protests and the BMA's continuing planning for a ballot of members on industrial action.