(Matt Rourke/AP)

For the most part, home-Internet providers have avoided imposing data caps on their customers, leaving it to wireless carriers to restrict how much Internet you can use on devices like smartphones.

But now that's about to change in a major way: Beginning Nov. 1, Comcast is automatically applying a 1-terabyte data cap to residential broadband customers in nearly a dozen new states and parts of several other markets as well.

The changes mean you'll be charged a fee if you go over that monthly limit. While Comcast says 99 percent of users won't come anywhere near hitting the cap, the move will be a new restriction for potentially millions of consumers.

You can find the full list of affected markets here, but to highlight a few: The entire states of California, Colorado, Minnesota, Oregon, Washington and Wisconsin will be opted into the program by default.

You can opt out of the data cap in several ways. You can pay Comcast an extra $50 a month for unlimited data. Or, where it's offered, you can switch to Comcast's Gigabit Pro, an expensive fiber-optic service that costs $300 a month. You can also switch to a lower-end, budget plan like Economy Plus or Performance Starter, which offer slower service but let you avoid the cap. Corporate customers won't be affected by the plan, according to Comcast.

You may have noticed that the data cap rollout affects primarily Comcast's western and central U.S. footprint. It doesn't affect Comcast's northeast customer base, and that's intentional, said Charlie Douglas, a company spokesman.

Comcast has no plans to introduce data caps to the northeast, Douglas said. But he declined to rule out the possibility. “Our typical practice is, we will roll out different regions at different times,” he said.