When the Progressives were designing the ACA they took deliberate steps to avoid the “French Dodge” and put in strict rules around “controlled groups.” The French went down the ACA path decades ago, and their employers reacted rationally to the disincentives involved in having large companies. The first thing they did was limit growth of work forces, pared company size, hired long-term temporary laborers rather than employees (temporary laborers outnumber full-time employees to this day). Each time the government ratcheted the company size target downwards, the businesses dropped employment to fall below the attachment point of the law. When the number got down to 50, the French realized they were in a race to the bottom and stopped. They had fragmented many companies and cut into the critical mass of size needed to succeed in the euro markets. What to do? Voila! Allow companies to have common ownership and control, pretend they are still small and separate, and let the company skirt the law; a small price to pay for economic performance.
Here is a article by Steven Saraisky of Cole Schotz that does a very good job of laying out the major points regarding controlled groups. Note: Appears about mid-way through the article.