WikiLeaks released 29 audio recordings Wednesday that it said were taken from Democratic National Committee servers.
The voicemails, apparently copied from email accounts of seven DNC members, included party associates upset by Bernie Sanders' influence on the Democratic Party.
Reports say one caller did not want the Vermont senator to speak at the Democratic National Convention and opposed Sanders' choices for the party's 2016 platform.
The latest release is the second in the last few days. The release of 20,000 emails just before the opening of the Democratic convention prompted the organization's chairwoman, Debbie Wasserman Schultz, to step down.
WikiLeaks, a group that publishes original documents from anonymous sources and leakers, released the data without indicating its source. The emails were sent during a 17-month period between January 2015 and May of this year. The DNC announced in June that its systems had been hacked.
Democratic officials said at that time that hackers based in Russia were responsible for the intrusion.
The party organization has not commented on the emails released by WikiLeaks, but neither has it disputed their authenticity.
The manager of Sanders' political campaign, Jeff Weaver, said the emails confirmed "what many of us have known for some time," that DNC members were "actively helping the Clinton effort and trying to hurt Bernie Sanders' campaign.''