The labs will not just ignore the order, there are too many other levers they can try to pull to mess with those companies. Just for some examples, think about the number of employees reliant on visas that could be revoked, the government contracts that the hyperscalers hosting them that could be canceled, the certifications that all the data centers need to be hooked up to the grid, the tariffs that could be put on critical components, the IPOs that need to be approved by regulators, the bill introduced in Congress to seize 50% of their equity...

Lots of these moves would and should be struck down in court as an arbitrary and capricious use of administrative power. Some of them might not be, and in the meantime you're signing up for tons of trouble. A trillion-dollar company does not simply go to war with the US government.

A more mid-sized company that's not so intertwined, but not so small that they can't get a good legal team, might be another story.