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%.

A number of stocks fell in the afternoon session after bellwether United Parcel Service (UPS) reported weak earnings and withheld its full-year guidance, citing “macro-economic uncertainty” and low consumer sentiment.

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.