leagal ways to deal with bad feedback

Now a days company HRs are taking feedbacks of employees from last employer. In many cases employees leave due to bad boss and in such cases bosses give negative feedbacks of the employees. what are leagal options for such employee's if he or she has to loose a job just on the base of a negative feedback. In private companies emokoyees are being treated like bonded labours and if they wish to break free they cant go to a better company and get employment because of bad feedback.