Members of the Association of Secondary Teachers of Ireland take part in the first of seven planned strike days outside St Mary's College, Dundalkas

Teachers have ramped up pressure on Education Minister Richard Bruton over equal pay as more than 500 secondary schools shut down in the first in a series of strikes.

As the Association of Secondary School Teachers' of Ireland (ASTI) manned picket lines nationwide, the two other main teaching unions rowed in behind with a rally outside Leinster House in Dublin to demand action.

The Irish National Teachers' Organisation (INTO) and the Teachers' Union of Ireland (TUI) said the lower pay rates for staff who qualified since 2011 were " wrong and unconscionable".

They joined the campaign as ASTI bosses suggested the nuclear option of all-out school closures from Monday November 7 could be avoided if a short-term deal was agreed.

President Ed Byrne said a row over payment for substitution and supervision, which is running alongside the issue of equal pay for recent graduates, was never intended to force schools to close.

The Department of Education had warned that if a school is forced to close after the mid-term break because replacement staff cannot be found then all ASTI teachers in that school will be taken off the payroll, including those who signed a 2013 deal letting them opt out of the duty in return for less pay.

Mr Byrne said: "Our actions, other than the days of strike, were never intended to shut schools. It was intended to show we were doing duties that we were not getting paid for."

Mr Bruton had said the refusal to cover colleagues' classes and watch pupils at breaks was unnecessary.

But the minister is now facing demands from all three teaching unions to speed up pay equalisation, even though a deal has already been done for newly graduated national school teachers to have their pay boosted over the next year and a half.

INTO general secretary Sheila Nunan said two-tier pay is discriminatory, inequitable and unreasonable.

" Separate salary scales for teachers doing the same work are wrong," she said.

"Discriminatory pay scales are eroding teacher morale, sapping good will and breeding resentment. It is blatantly unfair and inequitable to pay workers differently for doing the same work."

TUI president Joanne Irwin said a lower pay rate for new teachers who started in 2011 or later i s wrong and unconscionable.

"Their work is as valuable as that of their colleagues who entered before that date and it must be valued equally in pay terms," she said.

Some 507 schools out of 735 closed.

The walkouts are the first in a series of seven planned strike days over seven weeks, running through next month and into December.

They include all but one of the 375 voluntary secondary schools; 91 of the 95 c ommunity and comprehensives; and 42 of the 265 in the Education and Training Board system which are mostly staffed by members of the Teachers' Union of Ireland.

All schools will reopen again tomorrow before closing for the mid-term break next week.

But it remains unclear what will happen in schools from Monday November 7 as teachers will turn up to teach but principals may not be able to open the school doors unless sufficient numbers of adequately vetted replacement staff are found to cover supervision and substitution.

ASTI members are refusing to do those duties after the Department of Education said their pay would be docked 800 euros after they stopped doing 33 hours of non-teaching duties and holding meetings outside of normal school timetables, known as Croke Park hours.

Meanwhile, Archbishop of Dublin Diarmuid Martin said he was concerned about the threat of a prolonged strike.

"That's not for the benefit of anybody. We have to have more concerted efforts to ensure that doesn't happen," he told RTE Radio.

"One also has to see that anything that disrupts the school system, the education of young people, is disastrous. There's no profession that knows that better than teachers themselves."

The ASTI has planned six other strikes in November on Tuesday 8, Wednesday 16, Thursday 24, Tuesday 29 and consecutive days in December on Tuesday 6 and Wednesday 7.

PA Media