SLF here. This sort of selection criteria has become pervasive in hiring for any job here in the U.S of A. A candidate for a job will list previous employers, but it is not possible to garner any information about actual abilities of the potential hire. If a previous employer is contacted and asked about the candidate all the company can legally say is that he/she 'worked here' with no indication of ability, whether they were fired, etc. Lawsuits are very successful if the previous employer mentions anything negative about the candidate, to such a degree no information about ability is ever revealed. Needless to say, there are responses that convey the status of the candidate by smoke signal.