Sporting bodies across Australia have thrown their weight behind gay marriage, with cricket the latest to add its support for same-sex unions as a contentious postal vote on the issue began.

So far, 15 sports organisations have signed an open letter urging marriage equality, including Football Federation Australia, Basketball Australia, the National Rugby League and several Aussie Rules clubs.

Those yet to show their hand include Tennis Australia and the Australian Rugby Union. Cricket Australia chief executive James Sutherland said his organisation's decision to sign-up was in keeping with its vision of being a sport for all.

"Cricket must be a welcoming environment for each and every one of us, regardless of gender, cultural heritage and — importantly in the current environment — sexuality," he said.