Are you one of those people who overstuff their carry-on bag? United Airlines is catching on to  you. The Chicago-based airline has installed new bag-sizers at airports.

The airline said it isn't changing its policy. It's just bringing awareness to passengers who may not abide by the rules by installing the sizers and emailings its frequent fliers to remind them about their carry-on rules, the Associated Press reports.

The airline has placed some of the sizers before security checkpoints. If an employee finds that a passenger's bag is too large, they send them back to the ticket counter, where they must pay a $25 fee and check their bag. The airline used to have passengers check their bag at the gate and they didn't have to pay a fee.

Some passengers believe that United is just pulling out these methods to collect more fees. However United argued that it is trying to speed up the boarding process.

Size limits have been in place for years but many airlines haven't enforced them. A passenger is allowed to bring one carry-on that fits in the overhead bins, so it must be 9 inches by 14 inches by 22 inches or smaller. They're also permitted to bring a personal item like a purse or computer.

Airlines introduced $25 fees to check a bag in 2008. As a way to avoid this, many passengers started bringing their overstuffed bags on to the plane and overhead bins started getting overcrowded.

Passengers may not be happy with having to pay the $25 fee to check their bag, but there may also be an upside to having less-crowded overhead bins.