The letter denounced the Brazilian government and called on the Inter-American Commission on Human Rights (IACHR) to declare human rights violations, order the cancellation of the project and pay damages.
Before the open of trading on Monday, Magal revised its 2005 income statement to reflect the cancellation of a turnkey project by an Eastern European customer.
Councils have also been affected by the government's decision to scrap the multi-billion pound Building Schools for the Future (BSF) project, which led to the cancellation of hundreds of schemes.