ACT for America staged rallies on Saturday in New York, Chicago, Boston, Denver and Seattle, as well as many smaller cities to denounce Muslims' law (Shariah), which the group says poses a threat to American freedoms.
The anti-Muslim protesters were met by counter-protesters who denounced their rhetoric as demeaning and insensitive.
In New York, nearly 100 people attended a rally near lower Manhattan. They were outnumbered by counter-protesters, and the two sides hurled insults across two rows of police barricades.
Police made arrests after fighting broke out between protesters and counter-protesters in several cities, including in St. Paul, the Minnesota, and Harrisburg, Pennsylvania.
Critics say ACT for America, which has been labeled a hate group by the Southern Poverty Law Center, denigrates Muslims and has repeatedly equated Islam with extremism.
Muslim advocates say the rallies are part of a wave of Islamophobia fueled by President Donald Trump, who called for a ban on Muslims entering the country during his election campaign.
Anti-Muslim incidents rose 57 percent last year, including a 44 percent jump in anti-Islamic hate crimes, according to the Council on American-Islamic Relations (CAIR), the country's largest Muslim advocacy group.
CAIR urged Americans to participate in one of several local educational events being organized in "a peaceful challenge to Saturday's hate rallies." It also warned Muslims to take extra precautions against potential violence over the weekend.
Liyakat Takim, a professor of Islamic studies at McMaster University in Hamilton, Ontario, in Canada, said Islamic law plays a role similar to Christian and Jewish law; as a guide to religious life rooted in the Quran.
Takim said most Muslims don't want to replace US law with Shariah, which offers guidelines or principles on how Muslims should live.