Teachers at Holton Primary School in Barry are striking after they say concerns raised over their management have not been addressed.
Members of the NASUWT, The Teachers' Union, say "inappropriate" treatment and staff restructuring has had an impact on their health and welfare.
The strike is planned to continue for six days.
The union is urging the employer to "take its duty of care to its employees seriously."
NASUWT members at Holton regret any disruption this strike action causes to pupils or parents, but they have been left with no choice other than to take this action due to the repeated failure of the employer to take seriously their concerns.
The local authority is being urged to address the issues.
That members have felt they had no option other than to take strike action is indicative of the strength of feeling amongst them. That they have to resort to such action in order to defend their statutory entitlements is appalling.
A spokesperson for the Vale of Glamorgan council said: “We are disappointed that the NASUWT has decided to take this course of action when lines of communication remain open.
"As an Authority, we remain committed to further engagement with the union in an effort to get this matter resolved at the earliest opportunity.”