Like Comcast, CenturyLink is charging the fees in part of its territory as a "trial" designed to gauge customer response before a wider rollout.
While Comcast is limiting monthly overage charges to $200, CenturyLink's overage fees will not exceed $50 per month.
But CenturyLink hasn't announced any option for residential customers to purchase unlimited data, and even paying the overage fees doesn't guarantee that customers can use the Internet as much as they like.
CenturyLink described the changes in an updated policy statement and "Excessive Use Policy FAQ."
The "usage based billing trial" will start July 26 in Yakima, Washington only.
There are different monthly limits depending on speeds, which are quite low on CenturyLink's DSL network.