Sparks flew again between U.S. Sen. Al Franken and his Republican challenger Mike McFadden over the use of U.S. steel to build the Keystone XL pipeline.

Iron Range politicians and union leaders took McFadden to task Friday over comments last week that he would opt for building the Pipeline with Chinese steel over U.S. steel if it were cheaper.

DFL state Reps. Jason Metsa, and Carly Melin and former Reps. Tom Rukavina and Joe Begich met with union representatives and several Iron Range mayors to decry what McFadden said at a Farm Fest candidate forum.

"Mike McFadden sent a loud and clear message to Iron Range families that he will not stand up for them in the Senate—not on jobs, not on American steel and not on the issues that matter to middle-class families, Melin said as the leaders held signs that read "support Jobs Here, Not China," according a state DFL party news release.

The McFadden campaign shot back, saying that Melin and Rukavina both voted for the new Minnesota Vikings stadium, which is made partially with non-U.S. steel, and that Franken voted for a loophole that allows Keystone XL to be built with non-U.S. steel.

"This is just a smokescreen to hide the fact that Sen. Al Franken will not endorse copper-nickel projects like the PolyMet mine near Hoyt Lakes," said McFadden spokesman Tom Erickson.

Franken spokeswoman Alexandra Fetissoff said there was no such loophole, and that Franken backed an amendment requiring American steel for the pipeline, which could be waived only if domestic steel increased the cost by more than 25 percent. The alternative, Fetissoff said, was a bill with a no buy America requirement.

"Al Franken voted for American steel," she said. "He has a strong record of standing up for Minnesota's Iron Range and for Iron Range jobs. He has made it abundantly clear that if the Keystone pipeline is built, he wants it built with American Steel and that's how he's voted."

Just days after the primary, McFadden has intensified his focus on Franken, for the second day in a row urging the Senator and other members of Congress to return to Washington immediately from their August break. On Friday, the McFadden campaign also criticized Franken for attending a fundraiser at a Lake Tahoe, Nev. spa with other Democrats and donors.