E-cigarettes could be banned in public places where children are present in a landmark vote in the Welsh Assembly.
The Labour-controlled government in Cardiff Bay is hoping to pass its Public Health (Wales) Bill in the Senedd on Wednesday.
If passed, the Bill would become a UK first and would restrict the use of nicotine inhaling devices in certain public places - such as schools, places where food is served and on public transport.
The move has been criticised by opposition parties and even divided opinion among health charities.
However, Health Minister Mark Drakeford insists the legislation will protect people from harm - and the curbs on e-cigarettes would make smoking less appealing to youngsters.
He said: "The Bill will help us to respond to a range of public health threats in Wales, including the risk of re-normalising smoking for a generation of children and young people who have grown up in largely smoke-free environments.
"It is the government's responsibility to create the conditions, which enable people to live healthy lives. This Bill strikes a balance between those actions which will make a big difference to people's health without intruding unduly on the rights of individuals to run their own lives."
Originally, the Welsh Government wanted to ban e-cigarettes from all enclosed public and work places.
However, its proposals were watered down to places to where children were present after a committee report split Assembly Members' opinions.
Labour is one seat shy of an overall majority in the Senedd and needs other parties' backing before it can pass legislation.
Both the Welsh Conservatives and the Liberal Democrats branded the government's plan as "nannyism" and said e-cigs could help people stop smoking.
Tory AM Darren Millar said: "Introducing this ban would be a huge step backwards for smoking cessation.
"Labour Ministers are totally misguided in their war on e-cigarettes and these measures will potentially undermine public health rather than improve it.
"We should be giving people a helping hand to quit smoking - not placing obstacles in their way."
Plaid Cymru have been less critical but said any legislation needed to be made "very carefully".
There has also been opposition from pro-smoking group Forest and even some health organisations.
Referring to the Bill's original form, Cancer Research UK said there was not "enough evidence to justify an indoor ban on e-cigarettes".
And in its evidence to an Assembly committee, The British Heart Foundation said: "It is heavy handed to regulate them as if they were cigarettes."
However, the British Medical Association Wales said it was in favour - arguing it is better to be safe than to be sorry.
And health body Public Health Wales' added: "We cannot sit around and wait a couple of decades to see whether or not the conclusive evidence that people might like to see is available before making a judgment."
The Public Health (Wales) Bill also includes measures on the licensing of tattooist as well as for councils to produce a local toilets strategy.