The federal Surface Transportation Board has paused its review of the proposed merger between Union Pacific and Norfolk Southern, requesting additional information about the deal's potential impact.

The merger proposal involves two of the nation's largest freight railroad companies. Union Pacific operates primarily in the western United States, while Norfolk Southern serves the eastern regions of the country.

Reports differ on the total value of the proposed transaction, with estimates ranging from $71.5 billion to $85 billion. The discrepancy in valuations reflects different methodologies for calculating the deal's worth.

The Surface Transportation Board, which regulates railroad mergers in the United States, has requested more information before proceeding with its review process. The agency evaluates proposed railroad combinations for their potential effects on competition, service quality, and the broader transportation network.

Railroad mergers of this magnitude typically face extensive regulatory scrutiny due to their potential impact on freight transportation across the country. The combined entity would create one of the largest railroad networks in North America, spanning coast to coast.

The pause in the review process is procedural and allows regulators additional time to assess the merger's implications for the rail industry and shipping customers.