A worker at Walmart corporate is asking thousands of fellow employees to take part in an organized “sick out” over the retail giant’s gun and ammo sales.

CNN reports that Thomas Marshall, one of three employees organizing the walkout, sent a message on a Slack and email chain “that included about 20,000 people.”

The message said:

In light of recent events, and in response to Corporate’s inaction, we are organizing a “sick out” general strike to protest Walmart’s profit from the sale of guns. Walmart is a company that has always placed its associates and customers first, and we have recently made great strides toward fostering a safe, inclusive, and progressive community. Last year, Walmart raised the minimum age to buy a firearm or ammunition from 18 to 21 and removed products resembling assault-style rifles from its inventory. Walmart is still, however, the single largest retailer of firearms in the United States.

Marshall’s message also said, “We have made great strides already, but now we must organize to shape this company into a place we can all be proud of. As associates, we have the power, ability, and opportunity to change this company for the better.”

NBC News reports that Marshall’s message encouraged employees “to call in sick Tuesday … and take part in a walkout Wednesday.”

Another Walmart employee is urging those who cannot participate in the “sick out” to wear black that day in solidarity with those who can.