Civil society groups refused entry to Dungavel by the Home Office
Leading campaigners representing trade unions, churches and the third sector have been refused access to Dungavel detention centre.
The delegation wanted to visit the centre to assess the welfare of detainees some of whom have reportedly gone on hunger strike.
Lead by the Scottish Trades Union Congress (STUC) the representatives were declined access which has been confirmed by the Home Office.
The Scottish Refugee Council, the Church of Scotland and the Muslim Council of Britain were among the delegation.
Deputy general secretary of the STUC Dave Moxham said: "A number of organisations without a statutory role in inspection have been granted access to the centre, indeed the STUC was permitted to visit the facility in 2007.
We are forced to wonder why the government is so worried about organisations such as ours
"We are forced to wonder why the government is so worried about organisations such as ours being able to hear the experiences of detainees.
"We have always been clear that the problems for those detained in Dungavel may not originate with the running of the centre itself."
Dungavel, near Strathaven in South Lanarkshire, opened in 2001 and is Scotland's only immigration removal centre.
It is used to hold asylum seekers and other migrants before their removal from the UK or while their case is being assessed by the Home Office.
Last month a report by a group of MPs called for a time limit of 28 days on detention under immigration powers in centres such as Dungavel.
Sally Foster-Fulton, convener of the Kirk's church and society council, said: "It is deeply disappointing that the Home Office is refusing to allow us access.
"We, along with the STUC, want to listen to those held at Dungavel, hear their stories and offer whatever support we can.
"The mark of a good society is how we treat the most vulnerable within our borders. Making sure that compassion comes first is our only goal."