Laws that aim to protect businesses from environmental protests need "very careful" drafting to avoid a being struck down by the High Court, one of Australia's top constitutional lawyers says.

Prime Minister Scott Morrison last week proposed punishing environmental groups that encourage revenue-damaging secondary boycotts, which, for example, urge banks to withdraw funds from mining projects.

Prime Minister Scott Morrison wants to curb anti-business climate activism. Credit:John Veage

Constitutional lawyer Anne Twomey said widening secondary boycott laws would be a legislative challenge because the government would have to navigate a constitutional roadblock that stymies laws unfairly restricting political communication.

The High Court has leaned on the roadblock, known as the implied freedom of political communication, to prevent laws in the past that regulated political advertisements during campaigns and, more recently, restricted types of political donations.