A number of schools have confirmed that they will not open next Wednesday (5 July) as NEU members walk out in a dispute over pay.
Headteachers are writing to parents to tell them if they will be closed for the day because of the strike action.
The NEU balloted nearly 400 of its members, with 91% voting for a walkout.
Similarly, 86% of NASUWT chose to support the move, but the union has not yet set dates for strikes.
They have rejected a 7.9% pay offer for the 22/23 academic year.
The Education Department (CYPES) says it working closely with schools, but doesn't yet know the full extent of the disruption and is 'gathering details'.
The NASUWT began industrial action short of striking this week (26 June), which means some teachers will only fulfil their core teaching and safeguarding responsibilities and won't take part in lunch and after-school activities or meeting outside their contracted hours.
There is no end date set for the 'work to rule action, with headteachers saying that they expect disruption to their school's 'normal operation'.
NASUWT teachers will not cover for striking NEU teachers on 5 July.
Schools confirmed to be closed on 5 July include St Lawrence, St Martin and Trinity primaries and Hautlieu.
Letters to parents say:
"...Consequently, all schools around the Island have been asked to to assess and mitigate the potential impacts of the proposed strike. Our school has undertaken a detailed analysis to understand the impact of the proposed action on 5 July."
"As a headteacher, I am committed to doing all I can to avoid the interruption of the learning of our students, but my main priority is for their safety at school. I must ensure that there are safe levels of supervision and that first aid trained staff are available at all times."
Parents of children whose school will be closed next Wednesday are being advised to make their own childcare, work or other arrangements.
A full list of schools affected by strikes will be published on gov.je when is available.