Follow the money, as always. It's a bit hard to find any solid policy suggestions in the links above amongst all the fearmongering, but I'd wager that whatever their stated aims, they're not really pushing for reduced immigration, but rather for reduced protections for skilled migrants.
The more power employers hold over their skilled migrant workers, the more money they can make (from not only their skilled migrant workers but also from the rest of their workforce, who are now competing with the latter.)
The more power employers hold over their skilled migrant workers, the more money they can make (from not only their skilled migrant workers but also from the rest of their workforce, who are now competing with the latter.)