Teachers have voted for strike action at a school built on a landfill site after four members of staff were diagnosed with cancer.
Health concerns have been raised about Buchanan and St Ambrose High Schools in Coatbridge, North Lanarkshire, after instances of blue water coming from taps.
More than 11,000 people have signed a petition on change.org calling on North Lanarkshire Council to test every pupil, past and present, for toxins or contamination and demanding an independent investigation of the campus site to "check the site is safe from toxic waste".
The council has said the schools and the site are safe.
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The NASUWT union, which represents 12 teachers at special school Buchanan High, said it would take seven days of strike action later this month.
A union spokeswoman said: "Whilst the NASUWT is in dispute over the situation at the school, we have taken the unprecedented step of removing our members from the school site because of the serious health and safety concerns.
"The failure of the employer to act to address these concerns is unacceptable and our legal advisers are also taking appropriate action.
"No stone should be left unturned when the health of staff and pupils is at risk.
"The NASUWT should not be in a position where we have to take such action, but if an employer fails to act appropriately we will."
Its members at the school will strike from 20-21 June and 24-28 June.
'No link' between schools and cancer
Tests at the campus found higher levels of copper in the water in some areas of the school, which can lead to discolouration.
More than 1,800 metres of copper piping have been replaced with plastic pipes across the site, opened in 2012, which also includes Townhead Community Centre.
North Lanarkshire Council has set up a dedicated website with information about the situation at the campus.
It says: "Public health experts at NHS Lanarkshire have confirmed that there is no link between the site of Buchanan and St Ambrose High Schools and cases of cancer, following an investigation and assessment, which the council fully cooperated with.
"In addition, those experts have found no link to date with any other illnesses. The council will continue to provide any information required by NHS Lanarkshire.
"The safety of pupils and staff is the council's primary concern in any circumstances.
"There is no credible evidence to suggest that any serious illness has been caused by environmental factors associated with the school site or copper previously being present in the drinking water supply."
The site was used as landfill from 1945 to 1972 and domestic refuse and waste materials from the former Gartsherrie Steelworks were deposited there.
EIS union general secretary Larry Flanagan said that members at the schools had "raised significant and legitimate health and safety concerns", which the EIS has being pursuing on their behalf.
"In such a scenario, employers should act swiftly and positively by conducting tests to allay their fears and they should be open with the sharing of information and reports with health and safety representatives from trade unions," he said.
“Unfortunately, in this instance, North Lanarkshire Council’s response has been poor – in fact the EIS would go as far as saying that it has done far too little, far too late. For example, the EIS had to resort to making Freedom of Information requests to gain access to health and safety information and reports which should have been readily provided under the provisions of the Safety Representatives and Safety Committee Regulations of 1977. This only served to generate suspicion and mistrust.”
Mr Flanagan added: “The EIS is already actively pursuing legal remedy on behalf of some members and will be considering this aspect further at a meeting tomorrow. We have also engaged the services of an external expert company which specialises on reports on occupational hygiene and monitoring.
“We are very clear that North Lanarkshire Council remains liable for ensuring the safety, health and wellbeing of both pupils and staff in their buildings and for taking whatever steps are necessary to provide reassurance such as access to health monitoring.
“The EIS is willing to engage in constructive dialogue with North Lanarkshire Council as to how this reassurance can be provided but we would underline that the safety of pupils and staff is a top priority.”
A North Lanarkshire Council spokeswoman said: "Specialist doctors from the public health department of NHS Lanarkshire have confirmed that no incidence of cancer is linked to the schools.
"They have also confirmed that no other serious illness is connected to the schools or the site on which they are built.
"The council will liaise directly with trade unions on matters of concern to staff. All the facts demonstrate that the schools and the site on which they are built is safe."