Mr Dempsey intends to lower the blood-alcohol concentration [BAC] limit from 80mg per 100ml to 50mg per 100ml in forthcoming legislation.
The change would mean drinking a pint of beer could be over the limit.
Road safety campaigners say the reduced limit would save more lives on the roads. But some Fianna Fáil TDs believe it could do further damage to rural life and spell the end for many pubs.
Mr Dempsey will make a presentation to TDs at the weekly Fianna Fáil parliamentary party meeting in Leinster House tomorrow.
He has insisted, however, that he will proceed with the reduction – and says he has the support of the Cabinet to do so.
“This is hugely important,” Mr Dempsey told RTÉ Radio. “It’s about saving lives, reducing injuries and I’m absolutely committed to it, the Government is committed to it [and] it is in the Programme for Government that everybody unanimously endorsed last Tuesday at the Fianna Fáil parliamentary party.”
Mr Dempsey admitted that some of the backbenchers had “very serious issues” in relation to the proposed reduction. But he expressed confidence that he could win them over.
“A lot of them have said: ‘Show me the proof that we need to do this’... and I’ve no doubt that I’ll be able to do that on Tuesday,” Mr Dempsey said.
Several Fianna Fáil TDs have expressed their opposition to the measure. Tipperary South deputy Mattie McGrath said the proposed reduction was a “serious issue for rural Ireland” and that he would consider voting against it were Mr Dempsey to push ahead with the plan.
Taoiseach Brian Cowen said tomorrow’s meeting would provide the party with “an opportunity for a good, positive discussion, taking account of the policy position we have, which, of course, is to minimise deaths on our roads – the road safety strategy is an important one – and at the same time put forward practical policies that will address that and improve the present situation”.
A HSE report made clear the case for a reduction in the limit. The report said: “Whilst having a BAC of 80mg/100ml blood may mean the driver is not committing an offence, it does not necessarily mean that he/she is capable of driving safely... Drivers at the legal limit pose a risk at least 15 times greater than sober drivers. The relative risk of a drink-drive accident increases significantly after 50mg/100 ml BAC... Thus, lowering the BAC level to 50mg/100ml in Ireland should be implemented immediately.”