Project labor agreements, or PLAs, have been around since the 1930s. But they have become an increasingly common means for unions to exercise, directly or indirectly, monopoly power over labor markets since the U.S. Supreme Court gave them the green light in 1993 – in a ruling involving another massive Boston project. Less than 15% of America’s private-sector hardhat labor force currently belongs to a union, but PLAs ensure that many of the most lucrative projects are effectively union-only.