Violence flared in the Swiss capital of Bern as left-wing protesters tried to stop a pre-election campaign event by the nationalist Swiss People's Party.
The nationalist party is tipped to win the elections later this month
Police fired tear gas as demonstrators hurled rocks and bottles in front of parliament to interrupt a march and rally by about 5,000 SVP supporters.
The SVP has been criticised recently for its hard-line views on immigration.
Its campaign posters - showing white sheep kicking a black sheep off a Swiss flag - have stirred controversy.
The party, which has campaigned against minarets in Swiss cities, condemned the violence as contrary to the country's democratic tradition.
The disorder comes two weeks before the country's 21 October parliamentary elections.
Recent polls have forecast the SVP to emerge as the largest vote-winner.