UNION chiefs involved in the ongoing bus dispute are considering a 'no fares day' if negotiations at the Labour Relations Commission (LRC) break down.
Sources say such a protest could cost Dublin Bus and Bus Eireann over €1m combined in lost revenue while shoring up support among the public.
Transport workers previously staged a 'no fares day' in 2003 in a move that involved commuters seeing their fares waived as part of the industrial action.
Such a move may be adopted again if talks at the LRC fail to result in a breakthrough.
LRC chief Kieran Mulvey has admitted his officials are in a race against time in the bid to avert this weekend's strike action.
The decision by bus workers to down tools over the Bank Holiday weekend cost both bus companies hundreds of thousands of euro in lost revenue.
Sources involved in the negotiations have admitted that securing agreement this week will prove difficult given the range of different stakeholders involved.
The dispute centres around plans by the National Transport Authority (NTA) to put 10pc of bus routes out for private tender.
Unions will today demand guarantees surrounding the future employment of Bus Eireann and Dublin Bus workers if these plans go ahead.
A major sticking point in the talks also surrounds the prospect of further privatisation after 2019, when current Bus Eireann and Dublin Bus contracts expire.
Speaking to the Herald last night Mr Mulvey said the initial talks were "positive" and "fruitful".
But he admitted it will prove difficult to secure a breakthrough ahead of Friday, when the next phase of strike action is scheduled to take place.