Section 1. It is hereby declared to be against public policy for any employer to employ any person in an occupation in this commonwealth at an oppressive and unreasonable wage as defined in section two, and any contract, agreement or understanding for or in relation to such employment shall be null and void. A wage of less than $15.00 per hour, in any occupation, as defined in this chapter, shall conclusively be presumed to be oppressive and unreasonable, wherever the term ”minimum wage” is used in this chapter, unless the commissioner has expressly approved or shall expressly approve the establishment and payment of a lesser wage under the provisions of sections seven and nine. Notwithstanding the provisions of this section, in no case shall the minimum wage rate be less than $.50 higher than the effective federal minimum rate.