If the new prospective employer offers only 10% more than your current pay, you can always say, “no thanks, I need 20% more.” or walk away. This law is intended to shackle employers, and to put additional regulations into the process. If the employer can attract good people by not offering “market wages” (maybe they’ll hire some immigrants instead), then it is the prerogative of the employer to do so.
What you are saying is they trying to screw you from the git go and not pay market wages. Yet they want loyalty and hard work. This is why snakes like Bernie Sanders even exist.