Cam Newton claims his ex and baby mama, Kia Proctor, is blocking him from his kids and is suffering from substance abuse ... TMZ has learned.

In newly filed court docs, the ex-NFL star said he has concerns about the way Kia is parenting their four kids: Chosen, born in 2015, Sovereign-Dior, born in 2017, Camidas, born in 2018, and Cashmere, born in 2019.

Cam says he shares joint custody with Kia but claims Kia refuses to bring the kids to activities, claims she has substance abuse issues that have occurred around the kids, and says she has brought the kids to school late on numerous occasions.

He also claims Kia has blocked his access to the kids during her parenting time “for days at a time” and says she refuses to foster a relationship between their kids and their half-siblings.

Cam is asking the court to award him primary custody of the kids. At the moment, they share joint custody of the kids, and Cam pays around $7500 a month in support.

Kia has yet to respond.