Liberty is calling for a redefinition of Section 44 of the Terrorism Act 2000 after it was used to prevent the 82-year-old Walter Wolfgang from re-entering the Labour Party conference in Brighton last week.
Sussex Police has since admitted it used the section 600 times to stop people in the city during the week. Liberty believes this to be evidence of a worrying trend for the Act to be used against campaigners and ordinary people rather than suspected terrorists.
A spokesman for Liberty said: "Section 44 was drafted for situations in which, for example, police receive a tip-off that a bomb is due to go off in Parliament Square within a couple of hours. In those circumstances, it would be appropriate to use the Act to search people in that area.
"It is not appropriate to use it against a pensioner who has dared to express an opinion.
"We believe the Act should only cover areas where it is possible to stop and search everyone."