Llangefni's Ysgol Gyfun school teachers hold strike
An Anglesey high school has closed as teachers hold a one-day strike in a row over a cut in staff hours and an increase in class sizes.
Wednesday's action is being taken at Ysgol Gyfun, Llangefni.
Members of two unions, the NASUWT and UCAC, said there were also concerns about possible pay cuts.
Anglesey council said both the school and the education authority had been trying to find a resolution to avoid the industrial action.
In a joint statement, the unions said: "Staff have been targeted as a result of the manipulation of the curriculum, cuts to lesson allocation, increases in group sizes, the employment of temporary staff and constraints on option choices. Such treatment is unacceptable."
The council spokesperson said: "Every effort has been made to safeguard full-time posts.
"It is disappointing, therefore, to learn that the unions are frustrated by a perceived lack of co-operation from the school and local education authority."