The U.S. Department of Labor has setup guidelines for recruiters when searching for applicants online.  You can see the entire guideline pamphlet at http://www.dol.gov/esa/ofccp/iardwnld.htm.
Rule #1: When recruiters are vetting candidates online they are allowed to not consider candidates who aren't willing to do what is required to perform the job.  For example: If a candidate is not willing to travel, work overtime or work for a specific salary required for the job, the recruiter does not need to consider the candidate's application.
Rule #2: Recruiters are allowed to strategically limit the number of candidates they will consider.  For example:  If a recruiter has received 200 applicants, they are allowed to consider the first 20 (or any other amount chosen) and not consider the rest.  Or, they can randomly choose which candidates they will consider for the position. But they would not be allowed to exclude candidates based on age, gender or other discriminatory criteria.
Rule #3: Recruiters are required to properly use "basic qualifications" when searching for candidates online.  For example:  Requiring 10 years of experience for an entry-level legal position would be a misuse of "basic qualifications."  All basic qualifications that recruiter requires must be necessary to perform the job.