Opposition Leader Bill Shorten will attempt to introduce a marriage equality bill to the House of Representatives this morning.
The bill, which comes after a week in which marriage equality surged to the forefront of public debate, is not expected to pass as prime minister Tony Abbott has not allowed his coalition MPs a free vote on the matter.
On Sunday, Tony Abbott said the budget was the current priority for the government, and they would discuss marriage equality later.
"I've made it very clear that while this is an important issue the government has an absolute focus right now on getting the budget measures through parliament," he said.
However, it appears increasingly likely that a cross-party marriage equality bill will be submitted to the parliament later in the year.
Liberal MP Warren Entsch, who has been lobbying for reform within the party, told Fairfax Media he would "pop around and have a yarn with Bill" once the budget sittings were over on June 25.
"I'm confident we will get something up in spring," Entsch said.
Shorten will move the bill on Monday regardless – and in his speech, will say it's time for marriage equality.
"Today, this Parliament can change a law that no longer represents modern Australia…and pass a law of which we can be collectively proud."
"We can embrace a definition of marriage that respects, values and includes every Australian."
"We can declare, in the house of the Australian people - it's time. Time to make marriage equality, a reality."
Shorten will address lesbian, gay, bisexual, transgender and intersex Australians and their family and friends, saying marriage equality would make their relationships equal under the law.
"When someone has found not just another person they can live with, but a person they can't live without…then they should have the same right to the true qualities of a bond that runs deeper than any law."
"The same joy and sacrifice, care and compassion. The same rights and responsibilities."
Shorten will also specifically address young same-sex attracted Australians, saying "We are proud of you for who you are. You belong."
"You have an equal right to the hopes, aspirations and opportunities enjoyed by every other Australian, including the right to marry the person you love."
His speech will stress the importance of pushing for reform, saying change won't "just happen".
"We should never imagine this change is inevitable."
"We should never think it will just happen."
"We have to step up, we have to rise to this moment."