President Trump said on May 16 that he wants to put in a merit-based immigration system. The leading conservative Republican bill in the House is the Goodlatte bill, which does not include a merit point system. But a Senate bill submitted in early 2018 by Senator Cotton (RAISE Reforming American Immigration for Strong Employment Act) would introduce a point system (section 220). The RAISE Act point system is described here.
That point system, and one which President Trump likely has in mind, would essentially bar green cards for low formally educated immigrants. Some 27 million foreign-born people work in America, about 17% of the workforce. Among major occupations with no need (1) for a high school degree and (2) much contact with the public, immigrants fill about 40% of these jobs. They include jobs on farms, construction sites, warehouses, in kitchens, and for building cleaning and maintenance. Roughly half of the immigrant workers in these jobs are undocumented.