Nippon Steel Corp. is promising unionized workers of United States Steel Corp. that it won't send steel shipments from its overseas mills as part of its commitments to seal a $14.1 billion takeover of the iconic American company.

The commitment is among the undertakings highlighted by Nippon Steel's Executive Vice President Takahiro Mori in a Monday letter to United Steelworkers members at two key US Steel operations. Union leaders have repeatedly raised concerns that Nippon Steel's overseas footprint threatens the American industry — arguing that the Japanese steelmaker may one day find it cheaper to export certain steel to the US and replace some domestic output.