A group of inmates at a prison in Berlin have set up the world's first union for prisoners, in an attempt to campaign for the introduction of a minimum wage and a pension scheme for convicts.

Inmates at Berlin Tegel jail, where the union is based, work regular shifts in kitchens and workshops, which in the view of the union makes them "de facto employees, just like their colleagues outside the prison gates".

"Prisoners have never had a lobby working for them. With the prisoners' union we've decided to create one ourselves,"said Oliver Rast, a spokesman for the group.

In Germany, as in Britain, prisoners are excluded from national pension schemes and the national minimum wage, which in Germany's case is planned to come into effect in 2015 at €8.50 (£6.90) an hour. Inmates at Berlin Tegel earn between €9 and €15 per day, depending on their qualifications.

The Berlin union, which is registered as an association without legal status and claims to have collected numerous signatures within the prison, criticised the exclusion of prisoners from minimum wage plans.

It said the lack of pension schemes meant that many elderly inmates were released straight into poverty.

While there have been past attempts to set up union-like structures within prison walls, they have usually been short-lived and ceased to exist once individual inmates were released. In Britain, an organisation called Preservation of the Rights of Prisoners (PROP) was set up in the early 1970s but eventually faded away.

On Tuesday, Rast's cell was searched by prison staff, who reportedly confiscated documents relating to the foundation of the union. Rast was sentenced to prison in 2009 for his involvement in the leftwing organisation militante gruppe, which committed a series of arson attacks on government buildings between 2001 and 2009.

Sven Lindemann, a lawyer representing the union, described the search as an attempt to discipline and intimidate his client.

Berlin Tegel jail denied that it was trying to prevent the creation of a union and said the union founders had failed to alert prison authorities to its collection of signatures.

Frances Crook, chief executive of the UK's Howard League for Penal Reform, praised the Berlin initiative: "We want prisoners to develop civic responsibilities, and learning that work pays is a key stepping stone towards that goal. Why shouldn't they form a union to help them on that path?"