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.

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

Union Pacific and Norfolk Southern, two giants of freight transportation in the United States, have come together to form the nation’s first transcontinental railroad,