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.

Union Pacific Corp., North America’s largest railroad, is in advanced discussions with Norfolk Southern Corp. about a potential tie-up in what would be the industry’s largest deal ever.