The argument definitely belongs to the anti-immigration side. The pro-immigration side uses a higher percentage of pathos and emotional arguments to justify their views. The anti-immigration side uses a higher percentage of logos and socioeconomic arguments to justify their arguments.
It is a proven socioeconomic fact in a capitalistic economy that a huge influx of unskilled workers who do not speak the local language or speake it very little are willing to work more hours for lower salaries than local workers who speak the language. Industrialist usually use them to apply pressure on workers' salaries in order to keep them very low, especially in industrial agriculture.