The combination of two large rail companies would create the first coast-to-coast network, but the deal could reduce competition.

Union Pacific and Norfolk Southern confirmed that they are in “advanced” merger talks that would create a single U.S railroad with service stretching from the East to the West Coast. The Associated Press reported last week that the companies were discussing a tie-up but neither company acknowledged that until Thursday morning.

A combination could create the largest rail operator in the country with a sprawling rail network spanning the continent.