Norfolk stock traded as high as $288.11, but closed at $278, down 0.8%, while Union Pacific stock lost 4.5%, closing at $220.52. The S&P 500 added 0.1% and the Dow Jones Industrial Average lost 0.7%.

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 confirming they’re in merger talks that would create North America’s largest railroad, stretching service from East to West Coasts