Vice President Mike Pence's daughter Charlotte Pence showed her support Thursday for End It, a campaign by 16 non-profit organizations to end modern-day slavery and human trafficking.

It's an issue Pence has advocated for previously. Part of the proceeds from the sale of her 2018 book "Marlon Bundo's A Day in the Life of the Vice President" went to A21, a group fighting trafficking, and she participated in End It's red X campaign last year as well.

According to End it, there are an estimated 40.3 million people in slavery around the world, and modern-day slavery generates an estimated $150.2 billion annually in profits.

Lawmakers have taken steps to fight trafficking in the US. In March 2018, the Senate passed the Stop Enabling Sex Traffickers Act, to close a loophole that allowed websites where trafficking was facilitated to avoid responsibility for enabling it.