Exposing animal cruelty will become harder once a surveillance devices bill passes the South Australian Parliament, the Law Society has said.

The legislation has Government and Opposition support and is expected to pass when State Parliament sits on Thursday.

It would become a criminal offence to broadcast any video or audio obtained by covert means, unless a court agreed it was in the public interest.

In a letter to SA Attorney-General John Rau, Law Society president Rocco Perotta labelled it an "ag-gag" law.

He said it would prevent stories exposing animal cruelty from being broadcast, such as the ABC Four Corners report on use of live baiting in the greyhound industry.

"Whilst the bill was meant to address ... changes in technology and cross-border recognition of warrants, section 10 is about targeting undercover investigations into animal cruelty," Mr Perotta said.

"The society is of the view that section 10 of the bill, if passed, has the potential to have a harmful effect on animal welfare in Australia."

Greens MLC Tammy Franks is opposed to the legislation, saying it stops advocacy.

"It silences the proper role of exposing illegality, unethical behaviour, cruelty not just to animals but, according to the Labor vote today, specifically to animals," she said.

"The system currently isn't broken. It doesn't need to be fixed.

"The media operates ethically in this state and this kind of legislation will simply silence civil society and democracy."

The Attorney-General has not responded to requests for comment.