Trade associations representing various industries issued a letter Tuesday expressing “serious concerns” about a proposed merger between major rail companies Norfolk Southern and Union Pacific. “We write to express our serious concerns and reservations about the proposed merger between Union Pacific and Norfolk Southern,” said the letter, which came from trade associations representing manufacturing, chemical, energy and agriculture firms. “Past rail mergers have shown what happens when consolidation goes unchecked: service suffers, costs increase, and jobs disappear,” the trade groups wrote to the U.S. Surface Transportation Board. …The railroad companies, however, have argued that the merger will be a benefit to the country, improving efficiency and allowing for more routes. …In addition to the American Chemistry Council, signatories of the letter include the American Petroleum Institute, International Dairy Foods Association and the American Forest and Paper Association.