Members of the Independent Education Union will strike at the end of April if negotiations do not reach a positive conclusion.

“It is of great disappointment and ­frustration to our members that wage increases are well overdue and key issues remain unsettled,” IEU general secretary John Quessy wrote in an open letter to diocesan directors.

“The union is frustrated at the failure of employers to provide a response that would be acceptable to our members.”

Issues for negotiation include pay structure, personal/carer’s leave and professional development.

The highly controversial Catholic ethos clause – requiring teachers to hide their homosexuality and avoid using in vitro fertilisation – also remains unresolved.

“The union believes it has made some progress on the proposed ethos clause, however there is still a significant difference on some topics,” Mr Quessy said.

The IEU believes this particular clause will expose members to termination of employment targeting those in same-sex relationships, divorced employees and those who have remarried.

Teachers and staff who have used in-vitro fertilisation and support abortion could also come under threat.

“If this full day of industrial action goes ahead it will be the first time Catholic teachers have held a day-long strike in about 15 years,” Hunter IEU organiser Therese Fitzgibbon said.

“But there is a myriad of issues left to resolve within the Catholic Systemic Enterprise Agreement and the employers are just not responding so we’ve planned to take industrial action.”

Catholic Schools Office assistant director Gerard Mowbray said the Diocese of Maitland-Newcastle hoped an agreement would be reached and any industrial action averted.

“We are committed to keeping staff as up to date as possible with regard to this issue and we endeavour to pass on any new information as it comes to hand,” Mr Mowbray said.