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

The merger would create the United States’ first coast-to-coast rail network, spanning 50,000 miles and 43 states.

Union Pacific will acquire Norfolk Southern in an $85 billion deal, creating the first U.S. transcontinental railroad with service spanning 50,000 miles across 43 states.