In 1980, the railroad was purchased by U.S. Filter Corporation and was then sold in 1981 to Guilford Transportation Industries, which later purchased the Boston and Maine Railroad (and thereby the Portland Terminal) in 1983 and the Delaware and Hudson Railway in 1984. Initially Guilford operated the system intact, although the system now permitted run-through traffic between central Maine and Boston. By the mid-1980s, Guilford began to rationalize its system and fully one-third of Maine Central's trackage was eliminated, including the "Mountain Division" from Portland to St. Johnsbury, Vermont; the "Rockland Branch" from Brunswick to Rockland; the "Calais Branch" from Bangor to Calais; and the "Lower Road" from Augusta to Brunswick. Guilford also forced many management and salary changes, resulting in a major strike against the company in 1986. Guilford Transportation also moved the Maine Central's headquarters from Portland to North Billerica, Massachusetts, in the mid-1980s.