In every municipality with a population of 500,000 or over there shall be a board of examiners of mason contractors or employing masons consisting of 3 members, all of whom are practical masons. The members shall be appointed annually by the mayor or president, as the case may be, with the approval of the corporate authorities, before the first day of May. They shall hold office for a term of one year and until their successors are appointed and have qualified. They shall be paid from the treasury of the municipality such sum as the corporate authorities may designate.