Union Pacific and Norfolk Southern said on Tuesday that they have agreed to a merger to create a $200 billion rail giant based on their current market capitalizations.

The largest rail union in the United States said on Tuesday it intends to oppose Union Pacific's proposed $85 billion acquisition of smaller rival Norfolk Southern in regulatory proceedings, citing concerns about how the largest-ever buyout in the sector will affect U.

Omaha-based Union Pacific Railroad’s announcement Tuesday that it is acquiring the Norfolk Southern Railway — a move that would create the first transcontinental, coast-to-coast rail system — drew praise from Nebraska’s public and business leaders.