Smoking could be banned in town and city centres if Mark Drakeford succeeds in becoming the next first minister.
The Welsh Labour leadership candidate has included the plan in his manifesto for the contest.
Mr Drakeford also wants to ban smoking in outdoor areas of cafes and restaurants.
Currently smoking is banned in indoor public places.
It is also banned in cars where children are present. The ban is set to be extended to the grounds of schools and hospitals next summer.
Wales would be the first part of the UK to ban smoking in city centres if the proposals were implemented.
Ministers banned smoking in enclosed public places in 2007.
Mr Drakeford, considered to be the favourite to win the Welsh labour leadership election, tried to legislate for a partial ban on e-cigarettes in 2016, but the law was binned after members of Plaid Cymru withdrew their support.
His manifesto proposes to "extend [the] smoking ban to outdoor areas of cafes and restaurants and city and town centres".
"It is very important that we press ahead with reducing the level of smoking here in Wales," Mr Drakeford told BBC Wales.
He denied he would want to ban it outright.
"We already have bans on smoking on beaches in parts of Wales. This is a proposal to take this further," he said.
But UKIP assembly leader Gareth Bennett said: "As health minister, Mr Drakeford led a crusade against vapers, and now he wants to hit smokers by a ludicrous ban on people lighting up in outdoor places such as cafes."
Other proposals in the manifesto, launched in Barry on Monday, include installing drinking fountains across Wales.
He said he would consider requiring all new homes to have fibre broadband connections.
Mr Drakeford's document makes no specific mention of the M4 relief road - despite a decision looming on whether to go ahead with the scheme.
Instead, it says the government would "maintain our commitment to tackle congestion, particularly in areas such as on the A55 in north Wales, the A40 in mid and west Wales and the M4 in south Wales".
"Being in power is an opportunity, not a right", Mr Drakeford wrote.
"We must use every day we have, and every lever we have, to make Wales a more equal, fair and just society."