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 Corp. could reach an agreement to acquire Norfolk Southern Corp. and create a transcontinental rail behemoth as soon as early next week, people familiar with the matter said.The deal, which would be the largest deal ever in the rail industry,