Unfortunately ATCs, like most 'essential' gov't employees, don't have the right to a complete 'walk out' strike. The last time they did was in 1981 and Reagan fired the lot of them on the spot and 'decertified' their union.
ATCs have been thin on the ground for decades, a lot of it due to Reagan's actions. They never built the workforce back up. Sure, they're at 'minimum standards' but how old are those standards? Do they meet today's actual air traffic needs? I doubt it. And these days it seems that the very few who are qualified (like military ATCs leaving service) even want the job. I know I wouldn't. Too much pressure and not enough money for the enormous responsibility involved.