Plans for a smoking ban from 2 April face a late challenge from three AMs who want Wales' ban delayed until the one in England starts in July.
Assembly Members have voted for a ban on smoking in enclosed public places in Wales on 2 April, despite an attempt to delay it until a ban in England.
AMs have a free vote on the issue after a debate in the Senedd on Tuesday.
An attempt by one Conservative and two Labour AMs to delay the ban until July was defeated by 39 votes to 12.
The assembly government wants the ban on smoking in enclosed public places to come in as soon as possible.
It means the ban will go ahead on the assembly government's planned date of 2 April, three months before England.
Clwyd South AM Karen Sinclair said pubs in border areas could suffer if smokers cross to England, where they will be able to light up for a while longer.
A smoking ban has existed in Scotland since March 2006, two years after the Republic of Ireland introduced a ban.
The Welsh Assembly Government says it believes the ban will save at least 250 lives each year and has set aside £4m to implement a ban.
The Welsh Assembly Government wants the ban on smoking in enclosed public places to come in as soon as possible and has said it believes it will save at least 250 lives each year.
Ms Sinclair has joined forced with her Labour colleague, Vale of Clwyd AM Ann Jones, and Conservative Glyn Davies, AM for Mid and West Wales.
But Clwyd South Labour AM Karen Sinclair said pubs in border areas could suffer financially if smokers cross to England, after the ban is introduced in April.
Implementation dates
She said: "I've got quite a few villages where pubs are very close together across the border and I do worry that smoking commuters will choose to go across the border."
She said: "I've got quite a few villages where pubs are very close together across the border and I do worry that smoking commuters will choose to go across the border.
Ms Sinclair joined forced with her Labour colleague, Vale of Clwyd AM Ann Jones, and Conservative Glyn Davies, AM for Mid and West Wales ahead of the debate on the issue on Tuesday.
"And when you are talking about 13 weeks' difference in the smoking ban implementation dates, that's a significant length of time that could have a significant economic impact on the small pubs."
Following a free vote at the Senedd, a delay was voted down and the 2 April start date was backed.
The UK Government unveiled plans in October 2005 to give the Welsh assembly the power to ban smoking in public places.
Deputy Health Minister,John Griffiths said: "I'm quite clear that we want to have a situation where people working in cafes, restaurants and shopping centres, for example, are not breathing in other people's smoke and having their health damaged.
"And we want that new, much better situation, here in Wales as soon as we possibly can and, as I understand it, that date is the second of April."
