Teachers at a Cardiff primary school are striking over the suspension of four colleagues.
Three teaching unions, Unison and the GMB say the suspensions at Danescourt Primary School in October were "inappropriate".
They called for the head teacher to be suspended instead.
Cardiff council said the strike was "regrettable" when efforts are being made to "resolve issues". The school is closed on Friday.
The four teachers were suspended two months ago while the local authority launched an investigation into "personnel matters".
The council has stressed there are no child protection issues involved at the school, which has 348 pupils according to its last inspection report.
A senior head teacher was also brought in to assist the existing head until the matters are resolved.
The primary school was formed by a merger of Danescourt junior and infant schools in 2008.
An Estyn report said including the headteacher, there were nine full-time and ten part-time teachers at the school.
'Equally and fairly'
There were also 10 full-time and two part-time classroom support staff.
The teaching unions NUT, NASUWT, ATL and the two general unions said the three entrances to the school were to be picketed by 18 people from 0800 GMT on Friday.
Cardiff council said the strike meant it would not be able to guarantee the health and safety of children in the school on Friday.
A spokesperson said: "Senior officers of the council have worked closely with the governing body and trade unions to resolve the current issues at the school.
"It is regrettable that strike action is happening at a time when such efforts are being made.
"The education and wellbeing of pupils and staff there has remained our priority throughout this period.
"The council has a responsibility to ensure that all members of staff are treated equally and fairly and that due processes, in place to protect the whole school community, are strictly followed."
- 8 October 2010