The law, which was passed by the California Legislature and signed by Gov. Jerry Brown, bars licensed psychotherapists from working to change the sexual orientation of gay minors.
A three-judge panel of the 9th U.S. Circuit Court of Appeals issued an emergency order Friday putting the law on hold until it can hear full arguments on the issue. The law was set to take effect Jan. 1.
Licensed counselors who practice so-called "reparative therapy" and two families who say their teenage sons have benefited from it sought the injunction after a lower court judge refused the request.
The Associated Press contributed to this report.