Under the aforementioned Employee Polygraph Protection Act, it is illegal for private companies anywhere in the United States (not just Louisiana) to require or suggest an employee or applicant to submit to a lie detector test. It is also illegal for companies to use, accept or inquire about the results of lie detector tests that had previously been conducted on an applicant, or to take any adverse action (or threaten to take any adverse action) against an employee or applicant who refuses to take such a test.
There are, however, some exceptions. Polygraph tests are allowed to be used for people who are applying for or work jobs in the security industry, or in any field that involves handling drugs (such as pharmacy and medicine). And of course, polygraphs remain legal to be used as parts of criminal investigations, though they are not always admissible for use as courtroom evidence.