Source: BBCNews
Democratic presidential candidate Bernie Sanders' campaign has had its access to a critical voter database suspended following a data breach.
The campaign has fired a member of staff who had viewed data owned by the Hillary Clinton campaign in the party-controlled database.
The Sanders campaign and the Democratic party have blamed the software vendor.
The party has asked for a full investigation into the software.
Sanders campaign officials blamed a software glitch for allowing the low-level member of staff access.
However Congresswoman Debbie Wasserman Schultz, the chairwoman of the Democratic National Committee (DNC), said multiple Sanders staff members accessed Clinton campaign data and downloaded it.
The Sanders campaign said on Friday that it would sue the DNC in a federal court to restore its access to the voter data.
Sanders campaign manager Jeff Weaver called the DNC's actions "a heavy-handed attempt to undermine our campaign".
Strategically important information on voters is contained in the database, which campaigns use to decide strategy.
That data takes on a crucial role as campaigns prepare for early primary voting in just over a month's time.
Forbidding the Sanders campaign from accessing the database will significantly hamper its ability to reach out to new Democratic voters, says the BBC's Anthony Zurcher in Washington.