§ 206-b. Employment of females after child-birth prohibited. No owner, manager, foreman or other person in authority in a factory or mercantile establishment shall knowingly employ a female, or permit her to be employed therein, within four weeks after she has given birth to a child; provided, however, that any owner, manager, foreman or other person in authority of such establishment may employ a female or permit her to be employed within a lesser period after having given birth to a child if she presents to such person, (i) a written statement expressing her desire for earlier employment and (ii) a written opinion of a qualified physician that she is physically and mentally capable of discharging the duties of her employment.