Victorians do not want "a harmful public vote" on gay marriage, Premier Daniel Andrews has claimed in a strongly worded letter to Prime Minister Malcolm Turnbull calling for a free vote on equality.

And Mr Andrews has not ruled out pursuing state-based reform if the federal parliament fails to act on marriage equality.

"We have a proud history in this state of changing the law, and trying to be the progressive capital of our nation and that is not going to change," Mr Andrews told reporters on Monday morning.

Premier Andrews has written to Mr Turnbull "on behalf of" Victorians calling on him to stand up to those in the Coalition who do not represent a "fair and modern country".