I don't see what the problem is. This is perfectly legal. Private companies can do whatever they want with their own money.
Legal and moral are not the same. The law is largely beholden to massive corporations that are entrenched enough to abuse people in the pursuit of profit. One of the only levers we have to fight back is to call out these abuses and loudly call attention to them.
This is a ridiculous non-solution that has never really worked in practice. At best, it might revise the legal/PR strategies of the corporations and enables even more dishonesty on the part of various nonprofits who ostensibly "support" a related cause. More often, it's simply a big fat waste of effort.
Historically, organizing labor to withhold labor power to win political power for working people is in fact the only strategy that has actually worked. This is not what the actor/writer guilds are doing, though. They are merely bargaining for economistic industry-specific measures, not the political interests of working people as a whole.