In the simple terms, as per the title, it is protectionism. Without making an argument for either position, it seems a bit hypocritical when tariff critics, "You know this means the consumer will pay more, right?", reverse their position and demand protectionism for labor.
Of course there is much more nuance. Many H1Bs are not the mega-geniuses proponents allege. I lose interest when the argument turns towards IQ distributions and ID politics.
"Wage theft" is a bit spicy as well. Are employees entitled to their job at a given wage as some kind of Nativist birth right?
Comedian Sam Hyde had some interesting takes. I'm not convinced of his position, but he did well to illustrate how the dialogue around this issue isn't getting us there.