The doctors and other health professionals have gathered at Sydney's Town Hall to oppose the , which came into effect last week.
The legislation contains a provision that "an entrusted person" must not disclose protected information, with a breach potentially resulting in two years' jail.
The doctors, nurses and other allied health professionals said the secrecy provisions in the act present a huge ethical dilemma.
They said it is the job of health workers to speak up about abuse, yet the new laws mean any doctor who speaks out about conditions in Australia's detention centres may face two years jail.
Protest organiser Maria Singh said a petition calling for a repeal of the secrecy provision part of the act has collected about 400 signatures in one day.
Ms Singh said the petition will be sent to the Prime minister's office later today.
- with AAP