Protesters stand in front of the federal courthouse during the arraignment of Jeremy Hammond in New York, Monday, May 14, 2012.
CNN  — 

Jeremy Hammond, the Anonymous hacktivist currently serving his seventh year behind bars, has been called to testify before a grand jury in the Eastern District of Virginia but does not plan to cooperate, a group representing him says.

The development is an indication the US Justice Department is exploring additional charges against WikiLeaks founder Julian Assange.

In a statement, the Jeremy Hammond Support Committee said that “our assumption is that this the same grand jury that Chelsea Manning is currently being incarcerated for refusing to testify before.”

Manning, a former Army intelligence officer who leaked a host of files to WikiLeaks in 2010, is currently jailed for refusing to testify before an Eastern District of Virginia grand jury, widely believed to be related to an investigation of Assange.

Hammond, 34, was anti-Iraq War protester who hacked a number of sites he believed were tied to the military industrial complex and governments that didn’t respect human rights.

In 2013, Hammond pleaded guilty to hacking Stratfor, a Texas-based private intelligence company, as part of an Anonymous operation that gave the files to WikiLeaks. He received a 10-year prison sentence under the Computer Fraud and Abuse Act.

It wasn’t immediately clear how Hammond, who has had minimal contact with the outside world since his arrest, could have incriminating information on Assange. But as reported by Gizmodo in November, in sealed chats from Hammond’s case, he claimed Assange gave him a tool for parsing hacked emails.

Assange, who was arrested in April, faces 18 charges associated with Manning’s case, and has been accused of providing her with a tool to help her “in cracking a password.”

A spokesman for the US Attorney’s Office in the Eastern District of Virginia declined to comment. Federal prosecutors have been reticent to say who or what still may be under investigation.

CNN’s Katelyn Polantz contributed to this report.