Talks at the Workplace Relations Commission between Bus Éireann management and unions have concluded for the night.
Efforts to end the dispute over cost-cutting at the company will resume at 9.30am.
Progress on the discussions is said to be slow.
Sources say it is too early to say if there will be a breakthrough.
Unions have said nationwide pickets will remain in place for the duration of negotiations.
Speaking as he arrived at the talks on the 13th day of the strike, SIPTU's Willie Noone said the discussions would be hard and complex.
He also said management will have to once and for all show how they will contribute to cost savings, saying there needs to be a reduction in managers.
Mr Noone said he did not expect a resolution today.
NBRU General Secretary Dermot O'Leary said he was not going into the talks with any great optimism, but said there was a very strong resolve not to leave the talks unless there was something substantial to vote one.
Bus Éireann CEO Ray Hernan made no comment on his way into the talks.
In addition to the NBRU and SIPTU, three other unions are involved; Transport Salaried Staffs' Association; Technical Engineering & Electrical Union and the Unite trade union.
Minister for Transport Shane Ross has welcomed the attempt to resolve the dispute over proposed cost cutting at the company.
Both SIPTU and the NBRU have said their members will continue to place pickets on bus stations across the country during the talks.
1,900 Bus Éireann staff have been on strike since 24 March in a dispute over cuts to pay and conditions, which management insists are essential to avert the prospect of insolvency at the loss-making company.
The strike is costing the company €500,000 per strike day.