As a result of the Widdicombe inquiry, the Local Government and Housing Bill 1989 prevents employees from being elected to their own council. With Scottish local government going totally unitary next year, this will effectively debar the country's 300,000 council workers from standing for office.
At the moment, district council employees can be councillors in their region, and vice versa.
'It's not a question of if we are going to mount this challenge, but what are the best ways of highlighting the issues we are so concerned about - people's right to stand for public office,' said Mark Irvine, Unison Scotland's head of local government.
This year the government is due to prepare a report of how it is meeting its obligations under Article 25 of the UN covenant on Civil and Political Rights, which says all citizens should have the right and opportunity to take part in the conduct of public affairs. Unison could choose to submit evidence with that report.
Mr Irvine said no other European countries had such restrictive laws as the UK. In the Netherlands, for example, employees are eligible to stand, but if elected a commission of inquiry will look into their background to decide if there is a conflict of interest.
Although Unison is not planning similar action in the rest of Britain, Welsh regional secretary Derek Gregory said he was sympathetic to the union's stand in Scotland and would consider getting involved.