The head of the secondary teachers' union the ASTI has appealed directly to members to support a ballot that would see them cease working 33 hours of additional non-teaching time agreed under the Croke Park deal.

While the union had originally refrained from issuing an explicit directive to members on how to vote, ASTI general secretary Kieran Christie texted members on Monday requesting them to vote "yes" to the proposal to stop working the additional hours.

The message from Mr Christie references an intervention by the Department of Education “in the democratic processes of the union” as justification for the move.

Last week, the department warned that teachers risked losing up to €31,000 over the next four years if they followed through with the proposed industrial action.

In addition, department secretary general Seán Ó Foghlú said it was "extraordinary" that the union's central executive committee (CEC) had opted not to put full information on all the possible implications of such a vote before its members.

The trade union has been balloting secondary school teachers since May 4th on whether to withdraw their services for the extra 33 hours per year.

An ASTI spokeswoman told The Irish Times that the decision to direct members to vote yes was taken at its CEC meeting on Saturday.

The text was sent out to all teachers who the ASTI had contact details for, which was said to be the vast majority of union members. While many may have already voted, the ballot will remain open until May 18th.

“It was felt that the presentation of the issue was always made in such a way that a yes vote would be encouraged, but because of recent information posted by the Department of Education, the central executive council just felt it was necessary to be very clear about what the union was hoping to achieve from the ballot,” she said.

She also rejected accusations that members have not been thoroughly briefed on the possible financial implications arising from a yes vote.

"We feel that we gave all the factual information available to our members through Nuacht [the ASTI newsletter] and our website," she added.

Some within the union itself have been critical of a perceived lack of information given by the ASTI on the consequences of a yes vote.

The additional 33 hours of non-teaching time agreed under the Croke Park pay deal are widely-resented within the profession and regarded by many as wasteful and unproductive.

The ASTI is involved in another ongoing dispute with the Department of Education over junior cycle reform, with members refusing to conduct classroom-based assessments introduced under the new system.