Section one under the provisions:
1. Requires a reasonable attempt to be made to determine the immigration status of a person during any legitimate contact made by an official or agency of the state or a county, city, town or political subdivision (political subdivision) if reasonable suspicion exists that the person is an alien who is unlawfully present in the U.S.
That does not say anything about there having to be a lawfull arrest first. It requires the law enforcement officer to attempt to determine the legal status of the person during legitimate contact. How else would you determine that unless you were to ask for their identification? Demanding that would first require either a lawfull arrest, or a warrant.
If reasonable suspicion exists, a warrant should be obtained to search their person. The exception is if there is a lawfull arrest for another crime, you will get no argument from me there because that does warrant a search of their person. The language of this law appears to bypass that.