AT&T today announced that it will increase its data caps—and expand enforcement—on home Internet service. As a result, more customers will have to pay $10 overage charges for each 50GB they use beyond their monthly limit, similar to Comcast's data cap system.

AT&T will also let customers upgrade to unlimited data for an extra $30 a month. This is only necessary for Internet-only customers. People who purchase both AT&T Internet and TV in a bundle will get unlimited home Internet data at no extra charge. That applies to bundles with either DirecTV satellite or AT&T's wireline U-verse TV system.

Previously, AT&T enforced a 150GB monthly cap on its DSL network. On May 23, AT&T will expand enforcement of caps to U-verse Internet service, which brings fiber closer to the home to boost speeds, and to "GigaPower," its all-fiber service.

AT&T's blog post announcing the changes is titled "More Data, More Choices." AT&T also told Ars of the changes just before the announcement, saying, "Most of our U-verse home Internet customers will receive an automatic increase in their monthly data allowance, without having to do a thing: 250GB will increase to 300GB or 600GB, and 500 GB will increase to 1TB."

Previously, AT&T said cap enforcement wasn't necessary outside of its DSL network "due to the greater capacity of the U-verse architecture as compared to legacy DSL."

AT&T today told us that there are no changes to DSL data caps, which means some customers would still have to make do with only 150GB a month. That seems odd because the chart above shows that some users with DSL-like speeds of 768kbps to 6Mbps will get 300GB a month. We're trying to get a further clarification on this point.

Customers will get a few warnings before being charged overage fees. Overage charges will be capped at $100 per month.

AT&T's announcement went into some detail on how customers will be notified of overages:

In the first bill cycle when you reach 100% of your data allowance, we’ll update you via e-mail, but there will be no charges.

In the second bill cycle, we will notify you via email at 65%, 90%, and 100%, and still without charges.

In the third bill cycle, and each bill cycle thereafter, you’ll receive reminder emails at 65% and 90%. At 100% we will notify you and add an additional 50GB of data to your account for $10 each time you exceed the allowance. Customers will receive reminders about their data usage for the additional 50GB at 75% and 100%.

Beginning May 23, AT&T will update its online portal to let customers check their current usage data at any time. Hopefully it's accurate—some Comcast customers have discovered mistakes in Comcast's meter.

Comcast, the nation's largest broadband provider, has been enforcing caps in only parts of its territory in preparation for a possible nationwide rollout. It looks like AT&T will be enforcing caps throughout its territory when the new limits go in place.

This is not the first time AT&T has made unlimited data a perk of signing up for bundles. After purchasing DirecTV, AT&T brought back unlimited smartphone data plans, but only for people who purchase both AT&T mobile and TV service.

AT&T said that its home Internet customers "use just over 100 GB of data per month on average." But a sizable number would probably still have to pay overage fees. On Comcast's network, about 8 percent of customers exceed the 300GB limit.

Separately from data caps, AT&T has also been charging fiber Internet customers higher prices if they don't opt into usage tracking and personalized ads.