Unison will argue that political gags in the Local Government (Political Restrictions) Regulations 1990 interfere with workers' rights under Articles 10 and 11 of the Convention (freedom of political expression and association).
The union is challenging the gags on behalf of four members - Mobin Ahmed, solicitor, Hackney LBC, Ray Bentley, corporate policy unit, Plymouth City Council, David Brough, committee services, Hillingdon LBC, and Dennis Perrin, surveyor, Devon CC.
It has pursued the case through domestic courts since the restrictions first came into effect in May 1990.
Those earning more than£26,391 a year and those in posts deemed to be so-called 'politically sensitive' are affected by the scattergun effect of the ban.
In November 1993 the case went to the European Commission. In September 1995 the commission formally ruled that the application was admissible and referred it to the European Court of Human Rights for judgment. If the court finds that the restrictions inhibit rights under Articles 10 and 11, the government will have to repeal the legislation.
Unison will be represented by James Goudies QC; the government will be represented by the attorney general.
Unsion general secretaty Rodney Bickerstaffe said: 'We want this arbitrary and unnecessary political gag on local government officers removed. We have come a long way in our challenge and we believe it is now time for this new government of ours to adopt a new approach and rescind these regulations with good grace.
'It cannot be right that tens of thousands of employees are prevented from political expression, many with no right of appeal whatsoever. Blanket prohibitions which violate basic freedoms cannot be justified. They even prevent people from speaking out against local school or hospital closures. This Act has given new meaning to the expression taking a sledgehammer to crack a nut.'