Senators are usually elected for six-year terms with half up for election every three years. Following a double dissolution election, which clears all seats, the Senate is empowered to decide how six and three-year terms are assigned.

The "order of election" method being backed by the government and opposition sees the first six senators elected in each state serve the longer term while the bottom six are relegated and forced to seek re-election in 2019.

"12 senators are elected in every state. Under the methodology used on every occasion so far, the first six senators elected would get six years, whoever they are and whichever party they represent," Finance Minister and deputy government leader in the Senate Mathias Cormann said on Friday.

He told Sky News it "stands to reason" that senators who attracted more primary votes and preferences are rewarded and observed the method was used all seven times such a division in the upper house has been required.

While Senator Cormann did not explicitly say this was the government's plan of action, Fairfax Media understands it is the proposal and Penny Wong, leader of the opposition in the Senate, has confirmed Labor will back it.

The mechanism, labelled "unfair" and self-interested by Greens leader Richard Di Natale, guarantees full terms for 16 Coalition senators, 13 Labor senators, three Greens, two Nick Xenophon Team representatives, Jacqui Lambie and One Nation's Pauline Hanson.

The Greens' Senator Rhiannon, Liberal Democrats' David Leyonhjelm, Family First's Bob Day, law and order crusader Derryn Hinch, NXT's Sky Kakoschke-Moore and One Nation's three other senators are all endangered.

They will face a regular half-Senate election in 2019 when their terms expire, requiring twice the number of votes to get elected than in this year's double dissolution, which facilitated greater success for minor parties.

"This is consistent with the Senate's previous practice following double dissolution elections and reflects the will of the voters," Senator Wong said.

The Australian Electoral Commission has also provided advice, seen by Fairfax Media, regarding which senators would receive six-year terms using the alternative "recount" method - who would have been elected if it had been a half-Senate election.

Using this method - set out as a possible way forward under section 282 of the Electoral Act - Senator Hinch would have been elected at the expense of Liberal Scott Ryan in Victoria, and Senator Rhiannon would have beaten out Labor's Deborah O'Neill in NSW.

The top six for the other four states would be the same whichever method was used.

In a letter to Clerk of the Senate, Rosemary Laing, dated August 11, electoral commissioner Tom Rogers notes the Senate is not bound to follow the section 282 recount.

Senator Di Natale said the Greens support the recount method as "the fairer of the two" and "regardless of the outcome" for the party.

"The Labor and Liberal parties will stop at nothing to shut out everyone else from their cosy duopoly. Here they are again, voting together, to stop diverse voices in Parliament," he said, observing that both parties had previously advocated for the recount proposal.

Senator Hinch has threatened legal action if the major parties' method is adopted and has proposed an entirely new formula in which each party is guaranteed at least one six-year term.

With the Coalition and Labor's combined 56 votes in the 76-seat Senate, their preferred plan is guaranteed to pass.

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