Welsh Labour says it will not raise Welsh rates of income tax until "at least" the economic impact of coronavirus has passed.
It made the pledge in its Senedd election manifesto, which includes plans for a new medical school in north Wales and a new national park.
Welsh ministers can vary income tax rates by 10p in each band, but the powers have never been used.
Voters go to the polls on the 6 May.
The pledge means a rise in income tax is not completely ruled out.
Labour had promised no tax rises at the last election in 2016, but ministers have put the issue on the agenda in recent years.
In the manifesto, launched on Thursday, Welsh Labour vowed to tackle the backlog of postponed treatments and operations caused by the pandemic.
And it said it would reform council tax and open the first new national park in Wales since 1957, covering the Clwydian Range and Dee Valley.
Labour is fighting to keep its hold on the Welsh government, which it has led since the National Assembly's creation in 1999.
It was the largest party at the last election, and is defending 29 seats in next month's vote.
Party leader and First Minister Mark Drakeford said: "We've lived through an extraordinary 12 months, people I think want to have a government that they know is capable, competent and committed, and we'll finish that job, but we're more than that.
"We are a party with ambition for the whole of Wales to tackle the next crisis - the crisis of climate change and biodiversity loss."
In 2016 Labour guaranteed "not to increase income tax" in the following Senedd term.
In the 2021 manifesto the party said it will "not take more in Welsh rates of income tax from Welsh families for at least as long as the economic impact of coronavirus lasts".
Asked for further clarification a Welsh Labour spokesman said: "The impact of the pandemic will take time to overcome and we would need to see a strong recovery in personal finances across households before considering any increase in Welsh rates of income tax."
WALES ELECTION: THE BASICS
What elections are happening? On 6 May, people across Wales will vote to elect 60 Members of the Senedd (MSs). The party or parties that can command the support of a majority of members will form the Welsh government. Find out more here.
What powers does the Welsh Parliament have? MSs pass laws on many aspects of day-to-day life in Wales, such as health, education and transport. They also have control over some taxes. Defence, foreign policy and immigration are decided by the UK Parliament.
How do I vote? Anyone who lives in Wales and is registered to vote is eligible, so long as they are aged 16 or over on the day of the election. You can register to vote online.
In a BBC Radio Wales interview Mr Drakeford said Labour had kept Wales "safe" during the coronavirus pandemic and asked people to "give us the chance to complete the job".
Labour has been under pressure from some in its party to go further on extending free school meals, but the Welsh Labour leader defended plans not to extend the scheme to all children with parents on benefits. The scheme is currently restricted to families earning £7,400 or less.
In Thursday's manifesto the party said it would review eligibility, extending the scheme "as far as resources allow".
Mr Drakeford said more children would have eligibility "year on year", if Labour was elected back into power. He said Wales was the first part of the UK to guarantee free meals during the school holidays.
Mr Drakeford attacked Plaid Cymru's manifesto, saying it was "reckless" and "relied on borrowing money" - Plaid has insisted it is costed and independently checked. Mr Drakeford said all of the pledges in Labour's manifesto were "deliverable".
Asked why Labour had not used all its borrowing powers while in government, he said the party would "maximise the use" of borrowing in the next five years, but said making social care free at the point of delivery was "impossible".
"Everything we say, we can do," he added.
"When people are making choices... it is between a party who knows what it is to be in government, has the experience... and if they say something, it will happen."
Mr Drakeford said Labour would not do a deal with the Conservatives if no party won a majority at the 6 May vote, and ruled out supporting a Welsh independence referendum if a deal was done with Plaid Cymru to get Labour back into government.
Plaid has pledged to hold a referendum within the next five years if it is elected into government and has the support of the Welsh Parliament.
How do you offer a vision for a better tomorrow while at the same time emphasising that the crisis isn't over?
Mark Drakeford wants voters to let him "finish the job" of seeing Wales through the pandemic.
With risks of further waves of infection looming, he said Labour would use "every ounce of experience" to "keep you and your family safe".
But voters will be interested in what comes after the crisis too - and that's why he is so keen to shout about his "credibility".
In other words, you might like what other parties are offering, but can you be sure their sums add up?
Mr Drakeford, 65, had previously said he would stand aside as first minister if re-elected before the end of the first term, but would not be drawn on who he thought should succeed him.
The manifesto launch took place at Coleg Cambria in the constituency of Delyn - which Labour holds at Senedd level but lost at the Westminster election in 2019.
The party said there were six "ambitious pledges" at the heart of the election plans, including:
- The "biggest ever catch-up programme in our NHS and schools we've ever seen", and build a new medical school in north Wales
- The guarantee of a job or a place in education, training - or help to start their own business - for every young person aged under 25
- The guarantee of the Real Living Wage for care staff - which stands at £9.50 an hour and is more than the National Living Wage
- Abolishing more single use plastics and create a National Forest for Wales
- One hundred more Police Community Support Officers, bringing the number funded by the Welsh government to 600
- Creating thousands of new jobs in a "low carbon house building revolution", including 20,000 new low-carbon social homes for rent
It also promised a "new generation of integrated health and social care centres" and an "in-reach" child and adolescent mental health service in schools.
It says Welsh Labour would consult on a "potential Wales-only solution" to funding social care if the UK government "fails to bring forward a fully funded scheme".
The party also promised a moratorium on large incinerators, while Labour says it will lead Wales "in a national civic conversation about our constitutional future".
Welsh Labour said it would train 12,000 "doctors, nurses, allied health professionals and psychologists" over the five years of the next Welsh government term.
No commitment was given on whether there should be more Senedd members, but it said Labour would "build on the work" of a committee which recommended 20-30 more politicians.
Labour said its manifesto commitments were affordable and did not rely on increases in taxes controlled from Cardiff.
Health Minister Vaughan Gething had previously rejected the idea of a medical school in north Wales.