Thousands of nurses are expected to hold a demonstration in Parliament Square later in an ongoing dispute over the 1% public sector pay cap.
The rally is set to start immediately after Theresa May takes the first Prime Minister's Questions of the new parliamentary year.
The Royal College of Nursing (RCN) warned its members could strike unless the limit is removed.
It comes after a poll showed almost seven out of 10 people believe nurses are underpaid.
The survey also found the majority of people think there are too few NHS nurses to provide safe care for patients.
Speculation is mounting that the prime minister is preparing to end the cap for nurses, teachers and other public sector workers later this year.
The RCN's new YouGov poll of 1,624 members of the public found 72% believe there are too few nurses to provide safe care to patients.
Some 68% said nurses are underpaid, including 58% of those who voted Conservative in the last election.
Meanwhile, 57% of people said they would be willing to pay more tax to make the NHS safer - including a majority of Tory voters.
A recent report by the RCN revealed the number of vacant nursing posts in England alone stands at around 40,000.
RCN chief executive Janet Davies said: "The public can see the shortage of nurses for themselves.
"Ministers are significantly out of touch with public opinion. They should heed this warning, scrap the pay cap and help to recruit thousands more nurses for a safer NHS.
"Experienced nursing staff are leaving in droves - not because they don't like the job, but because they can't afford to stay, while the next generation do not see their future in an under-valued profession.
"If the Government fails to announce a change of direction in the Budget, then industrial action by nursing staff immediately goes on the table."
In May, almost eight out of 10 nurses polled by the RCN said they would be prepared to go on strike if the pay cap is not lifted.
Earlier on Tuesday, Transport Secretary Chris Grayling told BBC Radio 4's Today programme that the Government wanted to "provide people with additional pay" when the economy allowed for it.
The Treasury is due to send out letters within weeks setting out the remit for public sector pay review bodies for next year's pay round.
Shadow health secretary Jonathan Ashworth said: "Some Tories are hinting the cap will eventually be lifted but they voted against Labour's amendment to lift the pay cap earlier in the summer.
"It's simply not good enough. Nurses, midwives and paramedics should be valued and rewarded for the brilliant work that they do and the Government must make their plans on NHS pay clear now, before it is too late."
A Department of Health spokesman said: "As the Secretary of State has made clear, ministers are well aware of the pressures on frontline NHS staff, including nurses, who do a fantastic job.
"The support and welfare of NHS staff is a top priority, and the Government is committed to ensuring they can continue to deliver world-class patient care."
"We are helping the NHS to make sure it has the right staff, in the right place, at the right time to provide safe care - that's why there are over 31,100 more professionally qualified clinical staff, including over 11,600 more doctors, and almost 12,000 more nurses on our wards since May 2010."