NEW YORK (TheStreet) -- United Airlines (UAL) - Get Report is going to be enforcing its size restrictions on carry-on baggage more strictly, which may result in more passenger baggage fees.

VIDEO TRANSCRIPT:

Next time you're trying to sneak that over-sized carry-on onto a United Airlines flight, you might want to think again.

The airline is cracking down on carry-ons that exceed 9 inches by 14 inches by 22 inches, a restriction that's actually been in place for years, but hasn't been strictly enforced.  United says bags will be more carefully reviewed at the security checkpoint and at gates prior to boarding.

Now, if a carry-on is found to exceed the maximum dimensions, passengers will be forced to go back to the ticket counter and pay United's $25 fee for checked bags.

Some speculate that the move is part of an effort by United to collect more revenue through checked bag fees.  However, the Associated Press reports that United spokesman Rahsaan Johnson says the stricter enforcement is to address customer complaints about not being able to take their appropriately-sized bags onboard due to the lack of space taken up by over-sized carry-ons.

United Airlines is one of many airlines raking in extra revenue from checked bag fees.  The U.S. Department of Treasury says that U.S. airlines made $2.5 billion in baggage fees in the first three quarters of 2013 alone. Spirit Airlines (SAVE) - Get Report now even charges for carry-ons, while Southwest (LUV) - Get Report and JetBlue (JBLU) - Get Report still allow free checked bags per passenger.

In New York, I'm Brittany Umar for TheStreet.

-- Written by Brittany Umar in New York