Conservative think tank the Institute of Public Affairs has issued an ultimatum to Attorney-General George Brandis over his race laws proposal: do it properly or not at all.

In a formal submission to the Attorney-General, the IPA has warned Senator Brandis that, if he bows to critics and softens his attack on the laws, he would be better off leaving the law reform to a future, more courageous government.

Do it properly or not at all: George Brandis. Credit:Wolter Peeters

"George Brandis would be better off dropping his proposed 18C reforms entirely than proceeding with a watered-down version," IPA communications director James Paterson said.

"It would be a disaster if the Liberal Party put forward a version of 18C that left open the prospect of more Andrew Bolt cases."