A difficult year just keeps getting tougher for Japan's steelmakers, raising the possibility that the world's second-biggest producer could join the ranks of nations that have raised trade barriers to cheaper imports.

Forced to contend with an unprecedented glut of metal on export markets, and a yen that is doing them no favors, the nation's top mills swung to losses in the first quarter that ended June, warning that conditions could deteriorate. Forward three months, and the firms are dealing with new risks around the surging cost of a key raw material and a jump in steel imports.

Nippon Steel & Sumitomo Metal Corp., the world's biggest mill by market value, and JFE Holdings Inc. have both warned that raising prices is essential to absorb the extra cost from a likely doubling in the price of coking coal.