From Longman Dictionary of Contemporary Englishstep out of linestep out of lineBEHAVE#to behave badly by breaking rules or disobeying orders → step
Examples from the Corpus
step out of line• The boss is very tough on anyone who steps out of line.• The prisoners were warned that if they stepped out of line they would be severely punished.• He's not going to step out of line unnecessarily. 