42 CFR §457.560

1. (a)A State may not impose premiums, enrollment fees, copayments, coinsurance, deductibles, or similar cost-sharing charges that, in the aggregate, exceed 5 percent of a family's total income for the length of a child's eligibility period in the State.
2. (b)The State must inform the enrollee's family in writing and orally if appropriate of their individual cumulative cost-sharing maximum amount at the time of enrollment and reenrollment.