Glasgow City Council and North Lanarkshire Council have apologised and admitted that the action breached a law designed to maintain councils'
political neutrality. The heads were ordered to send out follow-up letters to parents underlining that position.
Letters with identical wording had been sent out from John Reilly, head of St Mungo's Academy in Glasgow, and Michael Currie, head of Our Lady's High, Cumbernauld. They highlighted Green Party opposition to Catholic schools, even though the party had stressed that it was only suggesting a debate on the issue.
Both letters concluded: "Please give careful consideration to the enclosed information and use your vote wisely on Thursday, 3 May."
A Glasgow City Council spokeswoman said the letters were "completely inappropriate", and that immediate steps had been taken to rectify the situation. Murdo Maciver, head of educational provision at North Lanarkshire Council, said the matter was being investigated. The follow-up letter said that the initial communication was "inappropriate", did not reflect the council's views and did not accurately reflect the Green Party's position.
A Green Party spokeswoman said: "We are disappointed that our position appears to have been misrepresented by many people and, if public resources have been misused, then clearly that will be a matter for the local authorities concerned."
The initial letters appended an article by Michael McGrath, director of the Scottish Catholic Education Service. He declined to discuss the matter, but stressed it would be "puzzling for any serious political party to make a commitment to destroy a system that's working well".
Neither headteacher wished to comment.