Comcast confirmed that it has been sending letters to broadband customers that will be affected by a new 1 Terabyte (1,024 gigabyte) usage-based broadband policy in several trial markets, including a new wrinkle that will limit monthly overage charges to $200.

The letter (posted here on the DSL Reports user forum) from Comcast Cable EVP of Consumer Services Marcien Jenckes, reiterates that the 1 TB plan takes effect in the test markets on June 1, while also noting that overage charges will not exceed $200 each month, “no matter how much you use – this is a new addition to the plan.”

Comcast announced the 1-TB plan in April, noting that customers who exceed that limit can buy additional buckets of 50 GB of data for $10 each, or move to a new unlimited data plan that runs an additional $50 per month. Previously, Comcast was testing a 300 GB data plan in most of its test markets.

Per the letter from Jenckes, customers who are on Comcast’s original unlimited data plan trial ($35 or $30 per month, depending on the market) can keep that rate through the end of 2016.

Comcast is currently testing monthly data usage plans in the following markets: Huntsville, Mobile and Tuscaloosa, Ala.; Tucson, Ariz.; Little Rock, Ark.; Fort Lauderdale, the Keys and Miami, Fla.; Atlanta, Augusta and Savannah, Ga.; Central Kentucky; Houma, LaPlace and Shreveport, La.; Maine; Jackson and Tupelo, Miss.; Chattanooga, Greeneville, Johnson City/Gray, Knoxville, Memphis and Nashville, Tenn.; Charleston, S.C.; Galax, Va.

Comcast has also updated its FAQ for the data usage trials that details policies governing the new unlimited data and 1 TB plans in those markets.

Customers who exceed the 1 TB limit during a given month will be notified by email and through an in-browser message that another 50 GB has been allocated to the account. Customers will also get in-browser and email alerts when they reach 90%, 110% and 125% of their monthly plan. Subs can also opt to receive mobile text notifications.

Comcast is also allowing for a grace period to help subscribers get used to the new plan. Starting June 1, all trial markets will move to a two-month courtesy program, meaning that customers will be subject to overage charges if they exceed the monthly data ceiling for a third time in a 12-month period. Previously, Comcast was granting a three-month grace period.

Under the plan being trialed, Comcast customers can’t roll unused data to a future month.

Comcast is still testing a “Flexible Data Option” for subscribers on its Economy Plus and Performance Starter tiers. That option, for lighter Internet users, provides a $5 credit if customers use 5 GB or less in a month. Customers who exceed that limit are charged $1 per gigabyte beyond the 5 GB limit, up to $200 per month (starting June 1).

Comcast’s FAQ also notes that the median monthly usage has been 60 GB per month during the past six months, and has previously said that more than 99% of its residential high-speed Internet subs don’t come close to using a terabyte of data in a month.

While Comcast has held that the trials are “based on principles of flexibility and fairness,” critics maintain that they in place to generate more broadband revenues while keeping growing over-the-top video competition in check.

When Comcast announced its decision to shift to a 1 TB usage plan, it drew some unexpected praise from Netflix CEO Reed Hastings, who tweeted: “Huge for me as a Comcast customer. Now I'll never be able to watch enough to hit my cap.”