You can file complaints with the FCC, but the FCC doesn’t actively monitor it. The biggest problem is that no matter how the law is written, they will find ways to abuse it. The law actually requires that the average volume of the ad not be greater than the average volume of the show. And it even specifies that the average is a running average, not just the peak vs lowest. But then loud portions of the show pump that average up. Like let’s say that during the credits you play really loud music, or really loud bloopers, well that would bump average. And if the commercial had a really long quiet period, like a long section where someone whispers the side affects a medication, well that bumps your loudest allowable portions up. They can also wait for the quietest part of a show to make the difference more significant.
And there’s much more that they can do that makes it seem louder, like frequency boosting and audio compression that are all totally legal. So, they can actually bump the apparent “loudness” of a commercial quite a bit and still be legal.