Germany’s highest court is considering whether to ban the far-right National Democratic Party (NPD).
The federal upper house (Bundesrat) took the case to the constitutional court in the western city of Karlsruhe.
The petition argues that the NPD is racist and anti-Semitic, and poses a threat to Germany’s democratic order.
A previous attempt to ban the NPD failed in 2003 because the judges dismissed evidence provided by state agents who had infiltrated the party.
The NPD is not represented at national level, but has members in the Mecklenburg-West Pomerania state assembly in former East Germany. It also has one seat in the European Parliament, held by former party chief Udo Voigt.
NPD members have joined regular “anti-Islamisation” marches by the right-wing Pegida organisation, based in Dresden.
The NPD’s anti-immigrant stance is part of widespread German anxiety about the influx of non-EU migrants, many of them Muslim Syrians, Iraqis and Afghans fleeing war and human rights abuses.
Germany severely restricts the power to ban a political party – a legacy of de-Nazification after World War Two.
Only the Bundesrat, Bundestag (lower house) or government can launch a banning procedure.
And only the constitutional court can impose a ban, if two-thirds of the judges back it.
Critics of the new case against the NPD fear that a ban could turn far-right extremists into martyrs. The party has about 5,200 members.
There are two post-war precedents for such bans in Germany. The West German authorities banned the Socialist Reich Party in 1952 and the Communist Party of Germany in 1957.
A banning order forces a party to completely disband and its assets can be seized, the German broadcaster Deutsche Welle reports.