AT&T says it is introducing a new unlimited data plan for its U-verse and GigaPower home Internet subs as of May 23.

It will cost an extra $30 per month for standalone Internet subs, but for those whose Internet is bundled with U-verse video or co-owned DirecTV satellite video service and paid for on a single bill, the unlimited data plan will be free.

AT&T is the latest major U.S. ISP to trot out an unlimited data option. Comcast is trialing an unlimited plan in several markets that costs an additional $30 to $35 per month, depending on the market. Comcast is also testing a soft cap that limits usage at 300 GB per month before charging $10 for additional buckets of 50 gigabytes, as well as a Flexible-Data Option for lighter Internet users. Comcast has not announced if it will apply these trials policies on a commercial basis.

Data caps are a focus in Washington of late, with the news of Netflix's efforts to slow traffic ostensibly to help customers with usage-based pricing plans and the FCC's investigation of zero ratings plans as carve-outs from such plans.

Most U-verse and GigaPower Internet customers will also be getting an automatic boost in monthly data allowances at no additional cost, ranging from 300 gigabytes to 1  terabyte, depending on their speed tier. AT&T says the average use is 100 gigabytes per month.

For U-verse Internet and GigaPower (AT&T's fiber-based platform) service, here’s now the speed tiers and data allowances stack up:

-768 kbps to 6 Mbps (300 GB monthly data allowance)

-12 Mbps to 75 Mbps (600 GB)

-100 Mbps to 1 Gbps (1 terabyte)

Under the new plans, AT&T is raising its previous monthly caps --  250 GB increases to 300 GB  or 600 GB, while the company's previous 500 GB ceiling is being raised to 1 TB.

AT&T notifies customers as usage approaches or exceeds data allowances, with no charge for a grace period of the first three months, but an extra $10 per 50 gigabyte overage in the fourth month and beyond. AT&T said the maximum monthly overage charge is $100.

AT&T has also set up ways for broadband customers to track usage, and, starting May 23, will introduce a Web portal that lets subscribers keep tabs on their current data usage.

In a blog post about the new usage-based policies, Bob Bickerstaff, VP of voice and data products at AT&T, noted that 300 GB equates to 100 hours of HD video streaming, while 600 is akin to 240 hours of HD streaming, and 1 TB is equal to about 400 hours of HD video streaming.

That’s notable because critics of usage-based pricing see the policies as a way to keep over-the-top video competition in check. AT&T, however, is preparing to launch a set of DirecTV-branded OTT video products in Q4 2016.

--Multichannel News technology editor Jeff Baumgartner contributed to this story.