Germany’s stepped-up efforts to ban some Islamic groups for promoting radical views have sparked a national debate over whether the government is violating the free-speech protections of the constitution it says it is aiming to protect.

The German government’s latest move to crack down on groups that promote extremist Muslim teaching came earlier this month, as dozens of police raided homes, offices and religious schools in the western German cities of Bremen, Braunschweig and Mönchengladbach. The security forces were seeking evidence that could lead to the banning of two organizations that officials say are calling for imposing Islamic law in place of German law.

Interior ministry officials allege that the groups, called Invitation to Paradise and the Islamic Culture Center Bremen, seek to undermine Germany’s parliamentary democracy by supporting the establishment of an Islamic theocracy within the country. A security official said the groups also allegedly support a strict form of Islamic justice, such as the execution of Muslims who convert to other religions or the amputation of a hand as a punishment for theft.

Sven Lau, deputy chairman of Invitation to Paradise, rejected the allegations, saying that his group hadn’t done anything illegal and that it calls on its members living in Germany to abide by German law. He described the group as a peaceful fundamentalist organization that believes in a strict interpretation of Islamic law, but said it advises members who want to live by its more extreme forms to live in Muslim-governed countries.

He wouldn’t detail what aspects of Islamic law the group specifically supports, but “we won’t amputate, stone or whip offenders” as punishment in Germany, Mr. Lau said. “The allegations aren’t relevant,” he said.

A spokesman for the Islamic Cultural Center Bremen said the allegations against his group are “unfounded.” He declined to discuss details of the allegations.

The raids come months after Hamburg officials in August closed the Taiba Mosque, which achieved notoriety in 2001 as the religious home for several members of the Hamburg terrorist cell that led the Sept. 11, 2001, attacks in the U.S. City officials said they ordered the closure because the mosque allegedly continued to serve as a meeting place for jihadists calling for holy war.

But the latest investigation marks a departure from previous crackdowns by German security and justice officials. German security officials are pursuing a ban of these two Islamic groups primarily because of the principles they espouse, rather than a suspicion of a link to terrorism.

A senior intelligence official said the outcome of the current investigation is unclear because neither Invitation to Paradise nor the Islamic Cultural Center Bremen has been linked to terrorism. Nor is the investigation into the groups related to the government’s warning of a possible terrorist attack in November, the Interior Ministry said.

The investigation has spurred questions over whether the effort could run afoul of German free-speech protections and further alienate pockets of Germany’s Muslim population.

The debate underscores the difficulty that Europe’s democracies face in trying to curtail Islamic extremism without violating their own constitutional principles.

“It is difficult to see the legal justification for a ban of the two organizations,” said Christian Busold, a legal adviser to Green party members who serve as representatives in Germany’s parliament. Although Mr. Busold said he had little liking for Islamic law, he said public rejection of the German constitution is still protected under German free-speech law and that such a ban made on that basis would likely be contested in German court.

An Interior Ministry spokesman said German law requires the ministry to investigate suspicions that organizations may be violating the constitution. The searches are a “suitable method” of obtaining evidence in an organization-ban investigation. No decision has been made on whether to ban the groups, he said.

Germany’s constitution, written after World War II and the fall of the Third Reich, makes allowances for restricting some forms of speech considered hostile to the country’s democratic order. German statutes, for instance, ban symbols such as Nazi swastikas as a violation of the constitution, and make Holocaust denial illegal.

Until now, such laws have mainly been used to curtail neo-Nazi activism. German authorities will “need to consider whether those restrictions apply” in the case of the Islamic groups under investigation, said Manfred Gnjidic, a lawyer who has raised German constitutional-law challenges to defend terrorism suspects.

In announcing the raids, Germany’s Interior Ministry said “a democracy shouldn’t wait until faced with a violent form of holy war before it takes action against organizations that oppose the German constitution.”

Dieter Wiefelspütz, a member of Germany’s opposition Social Democratic Party and a parliament representative, said the Interior Ministry had the duty to investigate allegations that a group was teaching intolerance or hatred. “In Germany, the tendency is to close too few rather than too many organizations,” he said.

One intelligence official warned that a potential ban could also shift part of Germany’s extreme Islamic scene underground to venues that are more difficult for security officials to monitor. “A ban won’t change beliefs,” the official said.

Amid the current investigation, both Invitation to Paradise and the Islamic Cultural Center Bremen continue to operate.

The Wall Street Journal