ACT Liberal senator Zed Seselja said his decision to vote against a bill allowing the territories to design their own voluntary euthanasia laws was "fundamentally not" a religious decision, and he understood not everybody would support his stance.

The Senate is today set to begin debating Liberal Democrat David Leyonhjelm's bill, which would restore the rights of territories to legislate on assisted dying.

Under the constitution, Federal Parliament can currently legislate on behalf of the territories.

Yesterday ACT Chief Minister Andrew Barr and Northern Territory Chief Minister Michael Gunner took out a full-page advertisement in The Australian newspaper, calling on federal senators to restore their jurisdiction's rights on the issue.

"Voting for this bill doesn't mean there will be assisted dying in the NT or the ACT. It will simply give Territorians the same right to decide on it as other Australians," the ad read.

But Senator Seselja said the private bill was not focused on territory rights, but human rights, and he would not support it.

"It's a conscience vote," he said.

"It's not a broader question of territory rights … we are talking about one issue."

And he conceded his views on handing over legislative control to the territories may be different if the bill was focused on another topic.

"If you were talking about a general look at the rights of a territory and how it should be able to legislate, of course different issues would be on the table," he said.

Senator Seselja said conscience votes by their nature were challenging and divided opinion.

"Of course there will be some people who will be very critical of my decision to vote the way I am, there will be other people who will be supportive of it," he said.

"You have to look very closely at the issue and that's what I've sought to do.

"I've read a lot of the debates when this last was considered when the Victorians debated this I've looked at some of the overseas experience where there has been assisted suicide over a number of years. That causes me grave concern."

Voluntary euthanasia 'crossing a very big threshold'

Senator Seselja said as a Territorian and despite self-government, some issues were simply overruled by the constitution.

"As a general principle, we have self-government [and] we should get behind that," he said.

"But the reality is that's the constitutional right that the Commonwealth has."

He also said his stance was "fundamentally not" guided by religion given the bill could allow the ACT to legalise voluntary euthanasia — though it has not yet officially indicated its stance.

"Many people of faith and no faith have come to the same conclusions about euthanasia," he said.

"The World Medical Association, for instance, talks very strongly against euthanasia, in the last couple of days I received correspondence from John Watkins, the former Labor deputy premier of New South Wales, on behalf of Calvary expressing real concerns about this.

"There are a range of voices and it's a fundamental public policy question that if you say 'in some cases we will deliberately take life', that is crossing a very big threshold."

The bill banning the ACT and NT from legalising assisted suicide remains in place, despite Victoria passing its own voluntary euthanasia law in October 2017.

Senator Leyonhjelm said the ban on the territories should be repealed because it was "not up to the Government to tell us where and when we bring [our lives] to an end.

"That's a situation that I don't think, is any business of the Government to be telling us 'no you can't, we know better than you'," he said.