Union Pacific, Norfolk Tumble as Regulator Pauses Merger Review

Shares of Union Pacific Corp. and Norfolk Southern Corp. slumped the most in more than a year after a key regulator paused its review of their planned $72 billion merger, potentially delaying what would be the biggest rail deal ever.

The US Surface Transportation Board accepted the companies’ merger application but said Thursday that further considerations would remain on hold until the companies submit additional required information. They have until July 27 to address matters “that are unclear or underdeveloped and require supplementation,” the board said.

Union Pacific fell as much as 5.2% as of 1:28 p.m. in New ...