Immigration and Customs Enforcement (ICE) has seized dozens of domain names over the past few days, according to TorrentFreak.
ICE appears to be targeting sites that help Internet users download copyrighted music, as well as sites that sell bootleg goods, such as fake designer handbags.
The sites are replaced with a note from the government: "This domain named has been seized by ICE, Homeland Security Investigations."
For instance, borntrade.com, 51607.com, and amoyhy.com have each been seized.
One of the site owners told TorrentFreak that his site was shut down without any notice or warning.
The effort comes as Congress considers the Combatting Online Infringement and Counterfeits Act (COICA). Critics, including Sen. Ron Wyden (D-Ore.) say it is too heavy-handed. He has vowed to put a formal hold on the bill.