The move comes in response to the recent suicide of internet activist Aaron Swartz, who faced federal charges.
The hackers claim to have a file on multiple servers ready for immediate release.
The group hijacked the website of the US Government agency responsible for federal sentencing guidelines today.
Members posted a message on the site demanding the US to reform its justice system or face incriminating leaks to select news outlets.
Anonymous is believed to be a collective of so-called "hacktivists" who oppose attempts to limit internet freedoms.
