Teachers at a school where four current and former teachers were diagnosed with cancer are beginning strike action over health concerns at the campus.
Concerns have been raised about Buchanan and St Ambrose High Schools in Coatbridge, North Lanarkshire, built on a former landfill site, after incidents of blue water coming from taps.
Members of the NASUWT union at Buchanan High are walking out on Thursday 20 to Friday 28 June.
NASUWT members at St Ambrose High will take strike action on 25, 26, 27 and 28 June.
The council has insisted the schools and the site are safe.
Buchanan High was closed to pupils on Thursday.
Gerard McLaughlin, head of education at North Lanarkshire Council, said: "Despite the facts being presented about the water being safe at the school campus and evidence demonstrating that it has been since early December and as recently as April 29, and that public health has stated there is no evidence to support a link between blue water at the school or the site itself and any serious ill health, the NASUWT has decided to take industrial action at Buchanan High School.”
He added: “Despite our disappointment that the NASUWT has taken this decision, we will remain in dialogue with trade union officials over the coming days."
The Scottish government last week set up an independent review to help address the fears of parents and teachers.
The review will look at health and safety concerns raised at the shared site, as well as the history, construction and maintenance of the campus.
The council insists the school is safe
NASUWT general secretary Chris Keates said: "Our members are suffering deep stress and anxiety about their health and welfare due to the failure of their employer to take the necessary action to provide assurances about the safety of the site.
"While the independent review promised by the Scottish government is a welcome development it still does not commit to a full comprehensive site survey which tests the water, air, soil and fabric of the building.”
More than 16,000 people have signed a petition calling for an investigation and for staff and pupils to be tested for toxins.
The site was used as landfill from 1945 to 1972 and domestic refuse and waste materials from the former Gartsherrie Steelworks were deposited there.
More than 1,800 metres of copper piping has been replaced with plastic pipes across the site, opened in 2012, which also includes Townhead Community Centre.