The U.S. enforcement of sanctions against three shipping lines Thursday comes amid growing signs of renewed economic friction between the two nations. If prolonged, it would be a serious blow to the firms, but damage to the overall Japanese economy is expected to be minimal.

Citing that Japanese port practices are inefficient and opaque, the Federal Maritime Commission is charging a $100,000 retaliative surcharge on each port call by container ships of three major shipping lines -- Kawasaki Kisen Kaisha Ltd., Mitsui O.S.K. Lines Ltd. and Nippon Yusen K.K. The sanctions are expected to total 5 billion yen a year.

The move comes as the two governments face potentially thorny issues, such as civil aviation talks to be concluded by the end of this month and the possible extension of a 1994 bilateral agreement on procurement by Nippon Telegraph and Telephone Corp. that expires Sept. 30.