Steel shipments fell last month as imports continued to surge.

U.S. steel mills shipped 7 million net tons in April, a 2.5 percent decrease from March and a 13.9 percent year-over-year decrease, according to the American Iron and Steel Institute. Cold-rolled sheets were down 7 percent, while hot-rolled sheets and hot-dipped galvanized sheets and strip were down 2 percent.

So far this year, shipments – or the amount of steel mills actually sell – are down 9.5 percent. U.S. mills have shipped 29 million net tons through the end of April, as compared to 32 million during the same period in 2014.

At the same time, steel imports have continued to rise. Import permit applications in May totaled 3.4 million net tons, a 3 percent increase over April, according to the U.S. Commerce Department's Steel Import Monitoring and Analysis data. Standard rail, tin plate, and hot-rolled sheets all posted major gains in May, as compared to April.

Line pipe, standard pipe and heavy structural shapes also are all way up year over year.

So far in 2015, total steel import tonnage is up 7 percent to 18.6 million net tons, while finished steel imports are up 20 percent to 15.3 million net tons.

Finished steel imports have captured 29 percent of the market share in May, and 32 percent year-to-date. That's way above the record market share imports attained last year.

Domestic steelmakers have blamed the flood of cheap imports for national layoffs and plant idlings that include U.S. Steel's East Chicago Tin in East Chicago.