Rail Megadeal Faces Scrutiny in New Document Request by US (1)

US regulators are seeking additional information about Union Pacific Corp.’s proposed takeover of Norfolk Southern Corp., an unexpected hurdle for the rail industry’s biggest-ever deal.

The Surface Transportation Board is requesting additional documentation from the companies on matters such as the potential impacts on competition and possible expansion related to the merger, according to a filing Wednesday. The agency is seeking a range of files, including documents produced both internally and by advisers.

The request — the first time the agency has done so in relation to a proposed merger, according to a person familiar with the matter ...