The letter, delivered to Assange at the Ecuadorian embassy in London, reads in part "As part of the inquiry, the Committee requests that you make yourself available for a closed interview with bipartisan Committee staff at a mutually agreeable time and location." 

Wikileaks' says their legal team is "considering the offer but testimony must conform to a high ethical standard," after which the whistleblower organization added a tweet linking to a list of 10 Democratic Senators who demanded in late June that Assange's asylum be revoked in violation of international law: