Papers will be lodged by the National Union of Teachers, at the high court in Cardiff today, to seek judicial review of the suspension.
The governors are backing the head, Carol Joynson.
The teachers were suspended on the first day of term in September and have not been allowed back to the 181-pupil school since.
They have received unanimous backing in a ballot from the other five classroom teachers of the school, all NUT members, and four support staff, members of Unison. They were joined on the picket line by teachers, parents, and pupils from other local schools.
The NUT said it had not been told the details of the allegations against the pair, but they are understood to include claims that the teachers acted unprofessionally, refused to follow school policy, failed to provide financial information about school visits, and disobeyed instructions from the head and governors.
David Hart, general secretary of the National Association of Head Teachers, which is representing Ms Joynson, said: "In our view the governing body had a right to suspend the two members of staff. It had more than adequate grounds for suspension. Clearly the NUT is upping the ante by taking a one day strike, and trying to overturn the suspension in the courts."
Governors rejected an offer by Caerphilly council to hold an inquiry, and began their own investigation. The NUT is refusing to cooperate because it believes the investigation is not independent. It said the case should go before Acas, the conciliation service. The council has urged the governors to reinstate the pair while inquiries are made.
Mr Hart said the local education authority had been "remarkably unhelpful and very unsupportive" by refusing to address the allegations.
Gethin Lewis, secretary of NUT Wales, likened the row to the Marjorie Evans case, the headteacher suspended without knowing the full details of allegations against her. She was eventually cleared. But he added: "This is different because then there were no agreed procedures. Here, there are agreed procedures and they haven't been followed."
He said the council should use its powers to take over the running of the school. "The governing body has had over eight weeks to sort out this mess but has failed to do so. The LEA must now step in to take over the school." The school will be open tomorrow but Mr Lewis said the union would consider further strike action if the suspension were not lifted.
