Walmart is asking customers to nominate their favorite teachers to win school supplies and a $490 gift card (approximately how much the average public school teacher spends out of pocket on classroom supplies).

For whatever reason, the promotion to give free supplies and money to teachers has the Washington Teachers' Union up in arms.

The Washington Post reports that Washington Teachers' Union President Elizabeth Davis called the promotion a "cynical coverup." Other union members called it "deceitful" and "bogus."

Their criticism focuses on the Walton Family Foundation's support for public charter schools. A union press release says the foundation is "one of the country's biggest funders of school privatization efforts, or charter schools." The foundation has given more than $2.3 million to the D.C. Public Charter School board.

"Walmart and the Walton Family have consistently sought to privatize our schools and destroy public education," Davis said.

Instead, the union is calling for a boycott of Walmart. "We're asking our members not to spend their hard-earned money at Walmart. It's important that public school teachers know that the dollars they spend at Walmart are being used to harm the very schools they work in."

But the criticism falls flat with both Washington, D.C.'s charter schools and traditional public school district.

"DCPS has increased our investments in schools every year for the last five years to ensure that our schools and classrooms have the materials needed for high-quality teaching and learning," District of Columbia Public Schools Spokeswoman Michelle Lerner told the Washington Post. "We also provide every teacher with $200 to supply their individual classrooms with school supplies."

Irene Holtzman, who runs a charter-school advocacy group in Washington, said the union's claim that charters take money from public schools is false. "All of our schools are funded on a per-pupil basis," Holtzman said. "Charters are not taking away money from DCPS."

About 44 percent of public school students in Washington attend charter schools, the fourth-highest share in the nation.

Jason Russell is a commentary writer for the Washington Examiner.