I study cartels, it's much more than that. Kind of stuff that can actually kill a company. It doesn't happen that often, and when it does the fine are usually so big they are diminished a bit. Companies are not stupid, when they are caught by the authorities, they trade informations. That's why we don't have nonsense like the american Verizon - Comcast - Warner cartel in Europe, where the american current FCC's boss is a former CEO of one of these company. Our authorities work whether nationals or EU. sometimes politicians try to intervene, but most of the time they are powerless (the only example I have in mind is when the french industry minister called the french competition authority to lower a fine on Arcelor-Mittal because they threatened to move all their industries out of the country if the fine went through, the fine ended up reduced by 90%, caused a small outrage).
The investigation process is very fun. It starts when someone tips you off, or when the actors of the market notice something wrong. Usually during the investigation, The first to spill the beans on the other cartel members leaves unpunished, the second, half the fine, after that, it's full tarif. Best part is they never tell you if you arrived first or second until the very end, they just wait until everyone panic while they go through all those files the company couldn't shred in time. The EU authorities are a bit different though, I don't know how they really investigate.
But the EU authorities are not soft, in the past, in the EU, we've seen huge fines. In 2012 7 national groups amongst which SD, Samsung, Panasonic, LG and SDI were condemned for 1.5 billion € (not 100 millions, 1000 millions) for a cartel on cathodic tubes, that's not the kind of fine your accounting team can plan ahead.
Now for the fine itself, the base amount of the fine is no longer a set pourcentage, it's decided in proportion to the value of the sales of the company, the gravity of the offense (cartels are the worst, typically), multiplied by the number of years the infraction survived. This proportion can be set at a level that can go up to 30%. BUT, it's not all.
The commission adds SYSTEMATICALLY a sum comprised between 15% and 25% of the value of the sales, whatever was the duration of the infraction (if the company participated in a cartel).