WASHINGTON, D.C. (CBS NEWS/KDKA) — The largest teachers union in the United States is threatening a boycott of Walmart over their decision to sell guns.

The American Federation of Teachers wants Walmart to stop selling guns and their potential boycott comes at a time when many parents and teachers are back-to-school shopping.

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“If Walmart continues to provide funding to lawmakers who are standing in the way of gun reform, teachers and students should reconsider doing their back-to-school shopping at your stores,” AFT president Randi Weingarten wrote in an Aug. 7 letter to Walmart CEO Doug McMillon.

The AFT has 1.7 million members nationwide, including 3,000 here in Pittsburgh, and according to them, their members spend an average of $500 per year on school supplies.

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The letter states opposition to the company’s decision to sell bulletproof backpacks and the shootings that took place in El Paso and Dayton. They also ask Walmart to fund gun buyback programs.

Walmart, however, says they have no plans to change their gun policy.

Company spokesman Randy Hargrove told CBS News, “No retailer is immune to violence.”

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It’s not clear when the threatened boycott would begin, but this is the busiest time for Walmart due to back-to-school shopping.