Entering  the country illegally is a crime punishable by 6 months in jail for the first offense and up to 2 years for subsequent entry. Being in the county illegally is only a civil matter for infractions such as overstaying a visa. 
I do not believe the established and law abiding will be targeted for enforcement but because of  the increase in border crossings since the election and the sake of future enforcement it only makes sense to allow agents the authority to use existing laws as they see fit.  Only when the border is secured can a meaningful program to legalize the productive residents be established. 
I guarantee once these people have a legal right to work they won't be doing the "jobs American's won't do" anymore  - they will quickly work hard  and take on the "jobs American's don't do well"