Senator Collins belongs to the Shop, Distributive and Allied Employees Association-linked faction known as the "Shoppies".

Some have suggested the Shoppies' influence has waned in recent years, with Labor increasingly adopting progressive social stances on issues like same-sex marriage.

"I do not represent a dying breed in the Labor Party. Those who come to our great party - or broad church - from a base of Christian social principles are not disappearing," Senator Collins told parliament.

"In some respects, we are stronger than during some periods over which I've served over the past two decades - just look at the recent euthanasia debate."

In August, she combined with faction allies Don Farrell, Helen Polley, Chris Ketter, and Deborah O'Neill to defeat legislation which would have given territories the right to make assisted-suicide laws.

"It serves the interest of some of those on the far-left and the far-right of politics to dismiss and diminish us, but I thank the many people over a wide spectrum who do not," Senator Collins said.

Senator Collins, who is leaving politics after first entering parliament in 1995, will be replaced by SDA union official Raff Ciccone.

She pointed to Labor's commitment to protecting religious freedoms in schools, as further evidence her grouping could still advance their interests.

In her final speech to parliament on Thursday, Senator Collins also welcomed the passage of the refugee transfer bill earlier in the week.

"I believe Australians are fair and decent people and that has come through ultimately in spades through my two decades here," she said.

"Australians do not want to see refugees languishing forever."

Senator Collins will reportedly be unveiled as the new head of the powerful National Catholic Education Commission after she formally quits politics on Friday.

Australian Associated Press