If the employer knows that their income won’t reach the minimum, their income tax doesn’t need to be deducted by the employer, and it’s not. Filling or not filling the taxes is irrelevant, I was pointing out that their income is usually exempt of filling, and such they usually request the employer to not withhold the taxes. It also happens with citizens, I’m not describing anything untoward, I’m just liking the unfortunate but probable poverty life with undocumented immigrants.