The Jones Act is one of those truly infuriating acts of protectionism that absolutely hurts everyone except a small and dwindling number protected producers and doesn't accomplish its stated purpose. It's sad that this sort of policy is once again in vogue.
It's not really about the unions in this case, it's just the few owners of some decaying old ship yards. There are only maybe 90 Jones Act ships in existence (you'll see different numbers). These are the sum total output of ~150 US shipyards. Its time to rip of the bandage, not only does this arrangement produce almost no ship it hobbles the domestic shipping industry, small ports, Hawaii, Puerto Rico, and anyone who wants to move goods or people by water between US ports.
