The conservative Christian group has launched a protest against the revelation that Northstar and his boyfriend Kyle Jinadu will marry.
They are also opposing DC Comics' announcement that one of its iconic heroes will soon be revealed to be gay.
"Children desire to be just like superheroes," reads a post on the One Million Mums website.
"Children mimic superhero actions and even dress up in costumes to resemble these characters as much as possible. Can you imagine little boys saying, 'I want a boyfriend or husband like X-Men?' This is ridiculous!
"Why do adult gay men need comic superheroes as role models? They don't but do want to indoctrinate [sic] impressionable young minds by placing these gay characters on pedestals in a positive light.
"These companies are heavily influencing our youth by using children's superheroes to desensitize and brainwash them in thinking that a gay lifestyle choice is normal and desirable. As Christians, we know that homosexuality is a sin."
The X-Man became engaged in this week's Astonishing X-Men #50, from Marjorie Liu and Mike Perkins, and will marry his lover in issue #51.
One Million Mums previously opposed the marriage of gay Archie Comics character Kevin Keller.
Writer Paul Cornell recently promised that his new Vertigo title Saucer Country would offend the organisation.