David Hogg, Parkland student and gun legislation campaigner, took to Twitter on Tuesday to encourage a boycott of BlackRock (BLK) and The Vanguard Group.

BlackRock and Vanguard, giant managers of exchange traded funds and other passive-style investments, are the biggest owners of publicly traded firearms makers like Sturm Ruger and American Outdoor Brands. The funds track stock indexes that include the stocks of the gun makers.

BlackRock recently said it had created new funds that would exclude those stocks for investors that wanted to avoid owning them.The new funds will not invest in American Outdoor Brands, Sturm Ruger, Walmart, Dick’s Sporting Goods, Kroger and Vista Outdoor, a BlackRock spokesperson told CNBC. The fund manager has also said it is in active conversations with gun makers about their businesses.

In a statement to Yahoo Finance, a Vanguard spokesperson said the firm “shares many individuals’ concerns about public safety and firearm access and hopes that policymakers take appropriate action to protect Americans from gun violence. Schools, churches and public spaces should always be safe places for all individuals.”

“Vanguard is taking action, meeting with the leaders of gun manufacturers and distributors. We want to know how they will mitigate the risks that their products pose and how they plan to help prevent such tragedies from happening again. We believe that boards and managements of gun manufacturers should disclose and reduce the risks associated with gun violence and the ongoing national debate on gun safety and control. We believe that when a business poses a risk to society, it can also pose a risk to investors. We are expressing this viewpoint directly with company leaders because we believe greater focus and transparency on these issues will ultimately benefit society and investors alike,” she added.

Hogg led a successful advertiser boycott of Fox television’s Laura Ingraham’s show last month after Ingraham publicly mocked his college acceptances. He survived the shooting at a Florida high school in February that left 17 people dead. Since then, he and fellow classmates have led a nationwide protest movement over gun violence.