Conflicts between a public company's top management and shareholders are seldom more intense than when an activist investor emerges with plans to make a substantial investment in the company's stock. These investors sometimes are hedge funds or "value investors" like Warren Buffett. Whoever they are, after they take a huge stake in the target company they have strong incentives to agitate vigorously for reforms that will increase the value of their investments.
Shareholders benefit from the reforms of corporate governance initiated by these activist investors. So does the economy generally, because the overall economy performs better when companies perform better. But managers are not so fond of this process because activist investors push incumbent senior managers hard to improve their performance. Occasionally they even fire them.
Since incumbent managers sometimes lose to activist investors in fair corporate elections, their preferred strategy for dealing with them is to hire legal talent and team up with friendly regulators to make new rules and to concoct anti-takeover devices like poison pills.