July 27 is the deadline for the railroads to supply more detail on competition, market-share projections and downstream merger effects before the board resumes its review, including environmental analysis.
Shares reflected the setback: Union Pacific fell 4.2% and Norfolk Southern dropped 5.4%, though an RBC analyst called the pause neutral for the deal's ultimate prospects.
The companies refiled in April after the STB sent back their initial proposal in January, and now expect closing in mid-2027 instead of April 2027.
The $85 billion merger faces opposition from business groups, rival railroads and labor unions, while the STB says it will spend up to a year on the public-interest review once the record is complete.
This railroad promises to take trucks off the road, but will it end up driving up prices for American families?
Could creating America's largest railroad also create its most catastrophic supply chain failure point?