ACT for America, a self-described grassroots organization focusing on national security, has scheduled protests in New York, Chicago, Boston, Denver and Seattle, as well as many smaller cities. Hundreds of people pledged on social media to attend.
At a rally on the steps of the Pennsylvania state capitol in Harrisburg, the atmosphere was tense.
Barricades and a heavy police presence, including officers mounted on horses, separated about 60 anti-sharia demonstrators from an equal number of counter-protesters, many dressed in black masks and hoods and chanting "No Trump, no KKK, no Fascist USA."
More than a dozen men belonging to the anti-government Oath Keepers were on hand, invited by ACT to provide security. Most of them carried handguns.
Leann Koons, 35, of Ricketts Glen, Pennsylvania, said she came to the rally "because I stand for women's and children's rights. I don't like how they treat women."
Chris Achey, 47, of Allentown, Pennsylvania, said he did not hate Muslims but believes that much of Islam is incompatible with Western culture.
"The Constitution is the law of the land," he said. "We have to be careful with who we let in the country."
The event ended without violence, and police said one counter-demonstrator was arrested.
On its website, ACT described sharia, which covers many aspects of Muslim life including religious obligations and financial dealings, as incompatible with human rights. It said sharia justifies the oppression of women and homosexuality, and advocates female genital mutilation.
But critics say the organization vilifies Muslims and has repeatedly equated Islam with extremism. In their view, the rallies are part of a wave of anti-Muslim and anti-immigrant sentiment fueled by President Donald Trump, who called for a ban on Muslims entering the country during his election campaign.