Facebook Inc. has taken down the pages of marijuana businesses operating legally in Alaska, continuing a practice that has targeted dispensaries in California, Arizona, Colorado and New Jersey.

The pages of at least six Alaska marijuana retailers were blocked in early July, about the same time Facebook founder Mark Zuckerberg was visiting the state for the Fourth of July holiday, according to the Alaska Dispatch News.

Alaska in 2015 became the third state to legalize recreational marijuana. Marijuana business owners, who face restrictions on traditional advertising, said they turned to Facebook to connect with customers given the lack of other options.

Facebook’s user policy bars content that promotes marijuana sales, even in states where it’s legal. The social media giant does allow marijuana advocacy pages, so long as they don’t promote sales.

A quick scan of Facebook Tuesday revealed pages operated by dispensaries in California, where medical marijuana use is legal, and in Nevada, which just launched commercial operations on July 1.

“Anyone can report content to us if they think it violates our standards,” Facebook spokeswoman Ruchika Budhraja said in an email. “Our teams review these reports rapidly and will remove the content if there is a violation.”

California, Facebook’s home state, will begin licensing commercial recreational marijuana businesses in January. Budhraja did not respond to a question about what the site will do should the hundreds—perhaps thousands—of licensees seek to maintain or launch pages. California would be the largest state to adopt recreational marijuana regulations.

Taylor West, deputy director of the National Cannabis Industry Association, said members of her organization talked to Facebook leaders about the page takedowns when they happened in Colorado about two years ago.

“We asked if they could please provide some clear rules about what does and does not violate their community standards,” West said. “We told them, ‘You’ll never find businesses that are more eager to follow rules.’”

Facebook at first “made all the right noises,” West said, but clearer guidelines never materialized. “It sort of leaves everybody up in the air,” she said.

Eric Goldman, a professor at Santa Clara University School of Law who runs the Technology & Marketing Law Blog, said Facebook’s actions are “completely logical” given that marijuana remains illegal under federal law.

“Publishing ads for an illegal item might expose Facebook to liability,” Goldman said. As a freedom of speech issue, “Facebook is the publisher and they can decide what to publish.”