If you strike against the US government as a public servant, yes you can be fired for breaking the law.[1]

Strictly within the context of the private world however, I don't know.

[1]: https://en.wikipedia.org/wiki/Professional_Air_Traffic_Contr...

Under the Wagner Act you can't be fired for concerted collective action in the workplace, if the goal of such action is to improve working conditions. That is a much broader protection than for just strikes (which are pretty narrowly defined).

But like you say, any corporation worth its salt can find ways to get rid of problem employees without violating the letter of the law even when it's not already planning big layoffs.