Talks are under way for a third day at the Labour Relations Commission aimed at resolving the dispute at Irish Ferries.
A SIPTU negotiator said the union was hopeful but not optimistic of reaching agreement by today's deadline.
However, he said the union would be offering significant savings to the company and could see no reason why agreement could not be reached.
Paul Smyth of SIPTU's marine branch said, however, that the company's proposals to re-flag its Irish vessels remained a major sticking point in the talks.
He added that SIPTU was receiving international support for its campaign against the re-flagging and outsourcing of labour.
The discussions at the LRC are being brokered by the National Implementation Body, which had set a deadline for today to reach agreement.
Irish Ferries vessels have been held up at ports in Ireland and in Wales while a stand off continues.
The dispute centres on plans to replace Irish jobs with lower waged agency staff.
Meanwhile, teachers' trade unions have said they are disappointed at the decision by the Minister for Education, Mary Hanafin, to dock the pay of teachers who attend Friday's day of protest in support of the workers at Irish Ferries.
Schools are expected to remain open, but public transport services in cities are expected to be disrupted during Friday afternoon.
