WASHINGTON -- Arizona Republican Sen. Jeff Flake is pushing for answers from the Pentagon about contracts between professional sports teams and the armed forces.

Minnesota's National Guard has spent more than $2 million since 2009 on marketing contracts with the Minnesota Vikings, the Wild and, to a smaller extent, the Timberwolves, according to public records.

In a letter sent late Monday, Flake said he felt like it was appropriate for the armed forces to use public money on recruitment, but what troubled him was that the Department of Defense is paying for hero tributes without disclosing that they are really marketing campaigns.

"While it may be appropriate for the National Guard or other service branches to spend taxpayer funds on activities directly related to recruiting, giving taxpayer funds to professional sports teams for activities that are portrayed to the public as paying homage to U.S. military personnel would seem inappropriate," Flake wrote to Defense Secretary Ash Carter and Gen. Frank Grass, who heads the National Guard Bureau. "Such promotions conjure up feelings of patriotism and pride for most sports fans, and the revelation that these are in fact paid arrangements is disappointing."

Flake is asking for the total amount the Defense Department has spent on "paid interactions" between service members at sporting events. He also wants details of those sponsorships. He is also asking for effectiveness numbers that the marketing campaigns have worked.

In Minnesota, National Guard enrollment has remained relatively flat at around 11,000, despite the recruitment and retention efforts.