In the letter, U.S. Steel warned customers that it might not be able to fulfill their orders and will try to identify alternative supply paths.

"We are working closely and are in continual contact with the United States and Canadian governmental authorities in an effort to expedite and obtain priority passage of our raw materials vessels on the Great Lakes," the letter said. "Unfortunately, passage has been prevented due to the ice conditions on the Great Lakes, which we hope will quickly improve as a result of recent warming temperatures. As result of this contingency, it is possible that our ability to timely fulfill your orders will be temporarily impacted. Please consider this letter notice of that possibility."

Berlin Metals President Roy Berlin does business with Gary Works and has been reassured that a flotilla of iron ore barges is on the way.

Iron ore freighters will be the first ships to pass through the Soo Locks in upper Michigan, but it is not clear when that will be, said Coast Guard Petty Officer 2nd Class Levi Read.