Section 22. If an employer, during the continuance of a strike, lockout or other labor trouble among his employees, publicly advertises in newspapers or by posters or otherwise for employees, or by himself or his agents solicits persons to work for him to fill the places of strikers, he shall plainly in type as prominent as the largest printed matter in the advertisement or poster and explicitly mention in such advertisements or oral or written solicitations that a strike, lockout or other labor trouble exists among his employees. Any such employer wishing to hire employees through an employment agency shall first notify such agency by registered mail of the fact that a strike, lockout or other labor trouble exists. No employer shall, during the continuance of a strike, lockout or labor dispute, hire a child without the written consent of his parent or legal guardian.