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.

Union Pacific and Norfolk Southern could announce a tentative merger agreement as early as this week, according to a published report. Bloomberg cited sources familiar with the talks in its report on Friday.

Union Pacific and Norfolk Southern are nearing a $200 billion merger that could reshape U.S. freight transport, raising hopes for efficiency and concerns over competition.