(a) A person may not: (1) violate the wage provisions of a public work contract; (2) allow or require an employee to work for less than the applicable prevailing wage rate; (3) except as provided in subsection (b) of this section, ask an employee or prospective employee to give anything of value to that person or any other person on a statement, representation, or understanding that failure to comply with the request or demand will prevent the employee from procuring or retaining employment; or (4) directly or indirectly, authorize a violation of this subtitle by any other person. (b) Subsection (a) of this section does not apply to any agent of a collective bargaining organization acting in collection of sums as allowed by the National Labor Relations Act.