States may soon have the authority to charge Medicaid patients higher co-payments, under new Affordable Care Act regulations proposed Monday.

The new rule would set a maximum $4 co-pay for any outpatient services used by Medicaid patients who live below the poverty line ($11,170 for an individual).

Up until now, the maximum co-payments have ranged between $1.30 and $3.90, depending on the actual cost of the service. In regulations, Health and Human Services contends that, since most procedures already cost enough to land in the range of a $3.90 co-payment "a flat $4 cost sharing maximum is reasonable."

While the change is not required by the Affordable Care Act, Medicaid head Cindy Mann explains that it's meant to anticipate the big expansion of Medicaid in 2014.

"It's not triggered by the Affordable Care Act itself and is not a change to the law," she told reporters on a Monday afternoon call. "It's prompted by the context of states expanding Medicaid."

The rule also allows Medicaid programs to charge a bit more for non-emergency trips to the emergency department. It will allow states to charge some higher income Medicaid recipients (those earning between 100 and 150 percent of the Federal Poverty Line) more for those non-emergent visits. Usually, states would have to seek a waiver to charge different prices for care delivered in different settings (the emergency room instead of the primary care doctor's office, for example).

Whether the change will save money remains to be seen: While states have already begun charging higher cost-sharing for non-emergency emergency room care, most research suggests that Medicaid patients' generally don't use the emergency department for routine care.