"One in five girls are missing school or extra-curricular activities because they lack access to period products... that's crazy!" he said while in Sundance on Friday.
The actor admitted that as a man, he "didn't think about it" until he was approached about being a spokesperson.
"It's one of the issues that I didn't really think about, and when I heard about it it was a no-brainer," he said. "I just thought 'let's just raise some awareness'. And in the meantime, get pads to girls who need them."
James, who is dad to four daughters — Olivia, nine, Annabel, six, Emilia, three, and Gwendolyn, who will be 2 in June, as well as seven-year-old son Joshua — said cis men simply don't worry about menstruation because they don't have to deal with it.
"Totally take it for granted," he laughed. "If it happened to men, it would not be an issue."
On his Instagram account, the "Dawson's Creek" star announced that for every view, comment or share of the call to action video, up to 2million pad donations will be made to girls in need.
"So... Dads. Remember when we first learned about periods in school, and everybody kind of squirmed and tried to pretend it wasn't happening? Turns out that approach can have a detrimental effect on our daughters," he wrote.
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"So let's step up and chip away at the stigma around this. Studies show that many young girls' confidence plummets around the time of their first period, but that engaging in your daughter's life, and treating her period like the normal, healthy thing that it is can help. A lot."
He called on followers to tag a dad (or coach, teacher, administrator or lawmaker or any guy you love): "Time to normalize what's normal!"