Union Pacific wants to buy Norfolk Southern in a $85 billion deal that would create the first transcontinental railroad in the U.S, and potentially trigger a final wave of rail mergers across the country.

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

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.