The four MSPs disrupted chamber business in making their G8 stand

The action against the politicians came after they staged a protest two weeks ago in the chamber, over the right to march on the G8 summit at Gleneagles.

SSP convener Colin Fox said the ban, which includes a suspension of salary, was unacceptable and disproportionate.

Two QCs have been instructed to begin an action in the Court of Session.

Mr Fox and three parliamentary colleagues, Frances Curran, Rosie Kane and Carolyn Leckie, took part in the pre-planned protest on 30 June and were subsequently ordered to leave the chamber.

The short demonstration concerned last week's G8 summit where the Socialists claimed the parliament had failed to secure the right for protesters to demonstrate outside Gleneagles.

The Presiding Officer George Reid later announced that they were to be banned from the parliament throughout September and lose their wages and allowances for the period concerned.

We have been denied any semblance of natural justice Colin Fox SSP convener

Mr Fox claimed that 41 members of the European Parliament had written to Mr Reid to protest at the severity of the sanctions imposed by parliament.

The Scottish Parliament's chief executive Paul Grice outlined the sanctions against the SSP MSPs at a meeting on Thursday.

Mr Fox said: "We have been denied any semblance of natural justice.

"We were tried in our absence without any kind of due process, right of appeal or any other basic human rights enshrined in law.