The Department of Education has been accused of a "campaign of vilification" against ASTI teachers in a bid to "whip" all public sector workers into line, .
AAA-PBP TD Richard Boyd Barrett is among a number of unions and political groups who have accused the Government of "locking out" teachers.
Hundreds of schools remain closed today as members of the ASTI union refuse to carry out supervision or substitution roles as part of their industrial dispute over pay and conditions.
Speaking this afternoon Mr Boyd Barrett said the Department and the Joint Managerial Body (JMB) have known for a long time that this day was likely to come and said they could easily have put contingency plans in place.
"Instead they have let come this far and then they have closed the gates, that to me it is a clear indication that they wanted an escalate the teachers dispute today and have locked the teachers out when those teachers arrived for work today," he said.
"It's absolutely a cynical move, there is a campaign of vilification being directed from the Department of Education against the teachers in order to whip all public sector workers into line, that's what's going on.
"Every worker out there should understand that it is in their interests to support the teachers because this is about the Government trying to keep a lid on legitimate claims for pay restoration for workers across the boards.
He said it was a "very easily solved dispute" and that teachers were keen to resolve it.
Sinn Féin's Eoin Ó Broin agreed that teachers had been locked out of schools this morning.
While Right2Water and trade union official Brendan Ogle said: "The legal and constitutional obligation to provide education to our children lies with the Government and is devolved to the Minister for Education, not the teachers.
"Teachers are employees who are employed by the State and where those children are not getting the education they are constitutionally entitled to the responsibility lies fairly with the Minister.
If the Minister has failed, which is manifestly the case today, to regulate the employment relationships with their employees to the extent that children are being denied their constitutional right to education then the minister is at fault not the teachers," he said.
ASTI president Ed Byrne has accused the Government of reneging on a deal to pay teachers for the time spent looking after pupils during breaks and free periods and when colleagues are unavailable to teach.
"This is to do with a rigid agreement they agreed ... they have reneged on that. It is not acceptable," he said.
"There is no sign of resolution. Let's be honest - schools are shut today because the department are trying to force us into Lansdowne Road. No other reason."
Mr Bruton said an offer is on the table for teachers to work the additional hour and in return trigger €1,500 pay for substitution time and quicker permanency and €6,500 pay rises for young teachers and new promotion opportunities.
"It beggars belief that the ASTI would close the schools indefinitely about their decision to refuse to work one hour per week over the 33 weeks that they work," he told RTE Radio.
"That's something that every public servant works. And some work more than one hour.
"They are trying to rewrite the entire approach to public pay in this dispute."
Mr Bruton said he was bewildered by the teachers' approach.
He said if other public servants took the same stance as the ASTI, it would cost the state €700m or 14,000 jobs.
John Curtis, general secretary of the Joint Managerial Body, which represents the 380 schools in the voluntary secondary sector, said only a dozen or so of its schools would remain open.
"This is unfair to thousands of students and their families who will be affected. We must get our schools open and our students back to their normal school routines as quickly as possible," he said.
The State Examinations Commission will keep exam plans under review depending on how long schools are closed.
The dispute is compounded by the planned series of walkouts by ASTI members over equal pay for new entrants with the next strike planned for Tuesday.
Mr Bruton claimed that plans to pay carers more money, give an extra €5 a week in benefits and for pensions and to employ another 2,500 teachers next year would be sacrificed if the attitude of the ASTI was replicated across the public sector.
The Taoiseach Enda Kenny says there will not be a loosening of the purse strings to increase public sector spending.
Hundreds of secondary schools are closed today as teachers seek a pay deal, while gardaí are also considering an offer.
Other public sector unions are likely to seek pay hikes of their own in the coming week.
However, the Taoiseach says a large increase in public spending would not be sound economics or socially just.
He said: "If we are to secure economic stability into the future, there can be no departure from the responsible management of the public finances. Not now, not ever.
"We cannot go back to the boom and bust, when-I-have-it-spend-it recklessness that brought this country over the edge."
A €796 payment for teachers is preventing hundreds of secondary schools from opening today.
The ASTI union says it is the amount they want to be paid each week for supervision and substitution duties.
However, the Department of Education is refusing to negotiate pay outside the Lansdowne Road agreement.
The ASTI's Vice President Ger Curtain says they want the original deal they were offered.
He said: "The payment for the supervision and substitution was covered by a circular in 2014 that stated quite clearly that for the school year 2016/2017 all teachers would be a paid a sum of €796 and in school year 2017/2018 a further €796."
Hundreds of secondary schools across the country are to remain shut indefinitely after crunch talks over a pay row collapsed without a deal.
Education Minister Richard Bruton said he is very disappointed last gasp negotiations with the Association of Secondary School Teachers' of Ireland (ASTI) over the weekend failed.
Minister Bruton has dismissed the row as just one hour a week of extra duties.
However, Diarmaid de Paor, Deputy General Secretary of the ASTI, says it is much bigger than that.
He said: "It is really about trying to bully us and our members into an agreement that they rejected.
"Our members decided that they did not want to be part of the Lansdowne Road Agreement and the department have, with a very heavy hand, withdrawn a lot of things from our members."
Mr Bruton said: "This will cause huge disruption for 200,000 students, and their parents, with particular stress caused for those in exam years.
"Asti have effectively decided to close hundreds of schools indefinitely, as a result of a dispute which essentially relates to one hour a week of additional duties.
"Monday's withdrawal from supervision and substitution duties, and consequent closure by Asti of hundreds of schools, is explicitly not about new entrants pay, but about the Croke Park Hours - one extra hour each week for the 33 weeks of the school year."
Asti has said its 17,500 members will refuse to carry out supervision and substitution duties as part of the industrial action over pay for supervision as well as equal wages for recently qualified teachers.
More than half of the country's 735 schools face closure as a result.
In a statement, the union said it is "regrettable" that the planned withdrawal from supervision and substitution will go ahead, citing "no progress" on key issues.
"Teachers who are members of the Asti will turn up for work as normal tomorrow but will not engage in supervision and substitution duties," the statement said.
The union said it will continue contacts with the Department of Education and Skills in the coming days.
Mr Bruton insisted a "good deal" is already on the table.
"I would again urge Asti to consider it seriously, so that we can end this dispute and limit the disruption to parents and students," he added.
"I am also disappointed that the Asti refused to cooperate with any contingency plans, both not allowing their principals to co-operate, and by not giving schools enough time to advertise, recruit and have external supervisors Garda vetted.
"As a result, hundreds of schools will be forced to close tomorrow to protect the health and safety of students and staff".