TUC leader Frances O'Grady has urged the government to use its influence to raise the plight of 23 people in Western Sahara given lengthy sentences after a military trial.
Ms O'Grady has written to Parliamentary Undersecretary of State Alistair Birt asking the British government to intervene and demand a fair civilian trial.
The former Spanish colony is now occupied by Morocco and there is an ongoing international campaign for self-determination for the mineral-rich region.
The 23 were arrested when Moroccan security services tried to dismantle the Gdim Izik protest camp - set up to highlight the Saharawis's percieved marginalisation and demand better jobs and housing - in November 2010.
Nine were given life sentence and the rest will be jailed for more than 20 years for the deaths of 11 security force members. Two Saharawis were also killed in the clashes.
Amnesty International has described the trial as "flawed from the outset" and called for an investigation into allegations of torture during the two-year pre-trial detention.