Communism must fundamentally be globally inclusive, with no discrimination to "race", nationality, or birth place. Being pro-worker from a communist perspective means inclusive of immigrant workers.
Marx is discussing population on a global scale, not immigration. And mind that overpopulation is not an issue when they billionaires are not sucking up all the world's resources for themselves and pitting the working class against each other to compete for the scraps.
You're talking from a nationalist perspective IE sneaking in Nazi shit in the backdoor of "worker's rights".
I mean, yeah, imperialists hate immigrantion into the imperial core (especially if they are brown and/or Muslim).
Nationalism and imperialism go hand-in-hand, along with anti-immigration policy.