Two of the most popular sites on the internet just entered the gun-control debate. 

In a sweeping move, Reddit banned all transactions involving firearms from its site Wednesday--just days after Google-owned YouTube quietly noted it would enforce tighter restrictions on certain videos that involve weapons.

YouTube on Monday posted updates to its policies noting it would ban videos promoting or linking to sites that sell guns and related accessories, as well as videos with instructions on how to assemble firearms, starting in April. Reddit's move prohibits the sale or trade on the site of guns, ammunition, alcohol, and controlled substances such as alcohol and tobacco. The site also banned an array of transactions involving sex, personal information, stolen goods, and falsified documents.

"Communities focused on such transactions and users who attempt to conduct them will be banned from the site," a Reddit spokesperson said in a statement. Among the communities (known as subreddits) that will be banned under the new rules are r/GunsForSale, r/GunDeals, and r/AKMarketplace.

The prevalence of gun discussions and transactions on Reddit has been a matter of significant controversy for years. The site had several active communities of firearms experts and enthusiasts--which drew ire from the press, including a 2014 Mother Jones exposé of the subreddit r/GunsForSale. Since 2011, r/GunsForSale has been a thriving community of licensed gun dealers, and over time morphed into an active marketplace where assault rifles, high-capacity magazines, and assorted other equipment were purchased and sold. At one point, a company obtained rights from Reddit to etch the site's logo, a small alien, onto AR-15s.

Reddit has banned users and subreddits in the past, but made those rule changes from a somewhat defensive posture. It did so when communities or individual users behaved so outrageously, or repeatedly violated existing site rules, that the company felt it needed to draw a line. Wednesday's announcement was different: No site rules were broken. It comes amid a shifting zeitgeist on gun control, and just two days before Saturday's March for Our Lives, a rally organized by survivors of the February school shooting in Parkland, Florida that left 17 dead. It's clear Reddit and YouTube are now proactively launching themselves into the center of the gun-control discussion.

The two sites are just the latest among many businesses that have taken public stands on the issue. Retailers including Dick's Sporting Goods and Walmart have recently taken steps to limit gun sales. Other technology companies have weighed in as well: Bumble, the Austin-based dating app, banned photographs of firearms from its user profiles. The company's founder and chief executive, Whitney Wolfe Herd, told The New York Times that making such a policy is often a fraught decision: "It's a very tricky battle we've chosen to take on," she said. "'But I'd rather pursue this than just ignore it."