The hearing was held by the House Government Reform Committee's Postal Service Subcommittee and its Government Management, Information and Technology Subcommittee and the Science Committee's Technology Subcommittee.
The dispute was started by more than 200 postal workers at the city's Tomb Street depot following difficulties between staff and management over disciplinary procedures and other issues in the north Belfast section.
The suit also names as defendants Johan Bruyneel, who had managed the U.S. Postal Service and Discovery racing teams on which Armstrong raced, and Tailwind Sports, which was the team's management entity, the Justice Department said.