The Association of Secondary Teachers in Ireland has told members they face the possibility of further strike action if members reject a Department of Education pay offer which has already been accepted by other teaching unions.
ASTI members are currently balloting on the proposals, but the union's leadership has recommended rejection.
The Department of Education has already warned that the latest proposals constitute a final offer.
If rejected, ASTI members will lose out on pay rises, increments, supervision and substitution payments, faster access to permanent contracts, they will not be entitled to posts of responsibility, and could face the prospect of compulsory redundancy.
In a post on its website, the ASTI told members that if they reject the proposed deal, they will continue their withdrawal from the 33 so-called "Croke Park" unpaid hours per year.
Their mandate for strike action on the issue of lower pay for recently qualified teachers will remain in force.
The union said members will also withdraw from supervision and substitution duties.
— Ingrid Miley (@ingridmileyRTE) January 20, 2017
While teachers belonging to the INTO and TUI have been paid for these duties since September because they accepted the Lansdowne Road Agreement, ASTI teachers who rejected the LRA have not.
An ASTI withdrawal from supervision and substitution duties forced many schools to close late last year on health and safety grounds.
The union notice said there will be an "orderly" withdrawal from the supervision and substitution scheme, though the memo noted that it may be necessary to continue doing those duties unpaid for a period of time to ensure schools do not close.
The ASTI directive on non-cooperation with Junior Cycle reforms will remain in place.
The ASTI notice also informs members that if the Department of Education proposals are rejected, members will be balloted to withdraw co-operation with initiatives in schools to be agreed by the union's leadership.
The message to members stated that if necessary, principals or acting principals will be balloted to refuse to co-operate with any request to identify teachers for redundancies.
It concluded by warning that in the event of an ASTI member being made redundant as a result of the redeployment scheme being withdrawn from ASTI members, the union will ballot for industrial action, up to and including strike action.
The ASTI ballot is due at the beginning of February.