Latest: The Union of Students in Ireland (USI) has condemned the failure of Bus Éireann management to resolve the dispute with their workers, which they said has caused "travel misery for tens of thousands of students".
What we know so far:
Update - 13.50pm: The Union of Students in Ireland (USI) has condemned the failure of Bus Éireann management to resolve the dispute with their workers, which they said has caused "travel misery for tens of thousands of students".
The USI have expressed their solidarity with the striking bus workers in the recent past, and say "nothing has changed" in their support.
They have urged the Minister for Transport Shane Ross to intervene in the dispute.
USI President Annie Hoey said: "This dispute has gone beyond the dispute between management and workers - it has created a complete gridlock for students seeking to get home and to college.
"Tens of thousands of students who rely on Bus Éireann and Irish Rail to travel around the country are now faced with Mother’s Day chaos and the prospect of facing into the exam season not knowing if they’ll be able to make critical classes.
"The failure to negotiate isn’t just causing inconvenience - it’s causing enormous anxiety and stress for people at the most difficult time of the year.”
She said that there are thousands of students who rely on Bus Éireann to go to college, work and even travel home at the weekends.
She said: "There are students who rely on the already poor public transport routes around Ireland to travel. We urge management and our Government to come to a resolution with workers, and firmly do not believe that workers should have their wages cut to plug the gap."
Update - 11.40am: Irish Rail has outlined what train services will see significant disruption today, because of the Bus Éireann dispute.
They have also advised that customers, who have booked a train today that has been affected, can travel on an alternative service for free, where available, using the same ticket.
Customers who no longer wish to travel today should email firstname.lastname@example.org for a full refund.
They also pointed out that Bus Éireann tickets are not valid on Iarnród Éireann services during the dispute.
Update - 10.55am: The organisation representing private coach and bus operators in Ireland has said that all services operated by its members will continue as normal during the industrial action by Bus Éireann workers.
The Coach and Tourism Transport Council of Ireland (CTTC), has said that the strike will not affect any of the 292 scheduled commercial services across the country operated by private bus companies.
National Director Kevin Traynor said that the private bus sector provides around two thirds of the scheduled commercial Bus and Coach Services across Ireland and deliver the majority of school transport services, under sub-contract from Bus Éireann.
The private transport sector also operates the majority of the country’s coach tourism services.
Transport Minister Shane Ross has said he is deeply concerned about the impact on the public of the Bus Éireann strike.
"It is now time for both sides to show this willingness can result in an acceptable and fair agreement that safeguards the company's future and all of those who rely upon it," he said.
Siptu's Willie Noone said the strike action had to be taken after management tried to enforce 30% pay cuts.
"Management wish to prepare the company for the future privatisation of public bus services by concentrating draconian cuts on ordinary workers," he said.
Update - 10am: Some of the extra trains put on by Bus Eireann for the Ireland v Wales game this evening will run.
The late night special from Dublin Heuston to Cork and Galway will run.
However, the service from Heuston to Limerick cannot be guaranteed, according to Irish Rail.
A list of cancelled services is on IrishRail.ie.
"Iarnrod Eireann has advised customers that there will be significant disruption to Intercity rail services today ... arising from picketing associated with the Bus Eireann dispute. Iarnrod Eireann is not a party to this dispute," the company said.
The Dart, Dublin commuter trains, Belfast and Westport services were among those operating a full schedule.
School buses have not been hit.
Update 9am: Bus Éireann management have refused to rule out putting the company into receivership.
They say the financial situation at Bus Éireann is grave and multi-million euro worth of cuts need to be made.
Chief Commercial Officer with Bus Éireann, Stephen Kent, says extraordinary measures may be needed.
"Well I think the directors will certainly - as I say - they have a duty to make sure the best interest of the company is served and they will have to take whatever necessary measures required to ensure the business remains viable."
Earlier: Bus Éireann passengers will have to make other travel plans today as an all-out strike is underway.
Buses stopped at midnight after drivers refused to work under the threat of pay cuts.
Bosses at the transport firm are warning they need to plug a multi-million euro hole in their finances.
But their claim that there is 'no basis' for talks led to unions escalating their action.
Seamus Boland of Irish Rural Link says commuters have been abandoned without warning.
"Well I think the short-notice hints at a very dirty strike which I think is going to affect people in a very bad way.
"Particularly people in rural areas, vulnerable areas, particularly people who have appointments, have medical appointments in Dublin and around the country - they depend on Bus Éireann."
Meanwhile, train services will face significant disruption because of the Bus Éireann strike.
There will be limited services on intercity trains between Dublin and several counties including Cork, Limerick, Galway, Sligo and Waterford.
There will be no services on Cork commuter trains or on lines between Waterford and Limerick Junction, and Limerick to Galway.
A list of cancelled services is on IrishRail.ie.
SIPTU organiser Michael Kavanagh has worked in Bus Éireann for 44 years.
He told our reporter on the picket lines at Broadstone Depot in Dublin they are not willing to accept any pay cut.
"You're now driving us back to wage levels we had in 1992 in the year 2017, and I'm not prepared to work for that.
"That's the reason my colleagues are here as well, we're not prepared to do it and as I said we regret it very much but there's absolutely nothing we can do about it."
Rush hour will be worse than usual around the country, with workers complaining they didn't get enough warning about today's strike.
A snap survey by recruitment website IrishJobs.ie says 40% of the workers they contacted are unprepared for the action.
Marketing director Safann McCarthy says it is also surprising how many people say they can't work from home and have no alternative but to find transport elsewhere.
"69% of the people we spoke to said that they have no option but to get into work. They have no option to work from home and I completely understand that it's dependent on what kind of job you're doing and what facilities you need.
"But, in an age where we are so socially contactable it's really surprising to hear that 69% of the people that we spoke to can't work from home."
Bus Éireann lost €9.4m last year, and SIPTU's Willie Noone says industrial action will stay in place as long as needed.
"Until the company actually decides to bring the unions in an engage, our members will be on the picket lines," he said.