Health groups are urging AMs to put pressure on the government to ban smoking in public places, describing it as a "top health and safety hazard".
A ban on smoking in public places has been introduced in Ireland
Action on Smoking and Health (ASH) claims that 130,000 people in Wales work in buildings where smoking is allowed.
An assembly committee is discussing on the issue on Thursday.
The assembly has voted for a smoking ban in the past but does not have the powers to introduce one.
According to government figures used by ASH - who are give evidence to AMs - 553,000 people in Wales work in places where smoking takes place in "designated areas".
Naomi King, Director of ASH Wales, said: "Smoking is a major health and safety hazard in UK workplaces.
"It causes hundreds of deaths every year across the UK, and many thousands of episodes of illness. It is also a major trigger of asthma attacks.
"The figures for workplace exposure in Wales show that proportionately more employees are exposed to other people's smoke than elsewhere in the UK."
Representatives of the British Medical Association Cymru Wales will also be giving evidence at Cardiff Bay.
The BMA had hoped that as part of its evidence 10-year-old Mared Jarman from Cardiff would be able to give her opinion on the subject - but AMs refused.
Instead the schoolgirl was watching the evidence from the public gallery.
The committee hopes to decide on a definition of a public place for the purposes of its work.
It will also receive a paper on its powers to control smoking in public places.
Since the end of March, smoking has been illegal in workplaces, including pubs and restaurants, in the Irish Republic.
The smoking ban means that if customers are caught smoking, proprietors will face fines of up to 3,000 euros (£2,000).