PRIME Minister Tony Abbott says the change in United States laws allowing gay couples to marry has not changed his mind on the topic.

The US Supreme Court ruled that the US Constitution should allow same-sex couples to marry. It means gay marriage will be legal in all 50 US states.

Mr Abbott said what happened in the United States was "a matter for the United States".

"As for our own country, obviously, there is a community debate going on," Mr Abbott said.

"I have views on this subject which are pretty well known and they haven't changed."

Opposition Leader Bill Shorten said the implications for Australia from the US decision were the same as when Ireland made the same decision.

Mr Shorten said American society was influential in Australia in its media, culture and system of government.

Mr Shorten urged Mr Abbott to take up the promise and allow a free vote in the Liberal Party on marriage equality in Parliament.

"Marriage equality should not be a party political issue," he said. - APN NEWSDESK