Greens senator Sarah Hanson-Young is facing a challenge from former senator Robert Simms for the prized top spot on the party’s South Australian Senate ticket ahead of the next federal election.

Mr Simms today wrote to Greens members in South Australia, urging them to vote for him in the party’s preselection process.

“Refreshing our Senate ticket provides us with an opportunity to reconnect with those South Australians who may have switched off from us,” Mr Simms said.

“With high unemployment and rising inequality, SA voters are desperate for change.

“Our state is ripe for a progressive revolution and the Greens are the party to deliver it. This should be our time.”

Mr Simms ran second on the ticket behind Senator Hanson-Young at the 2016 double dissolution federal election.

But with the Greens securing 5.87 per cent of the vote in South Australia, only one Greens senator was elected — meaning Mr Simms lost his spot in the Federal Parliament.

The No.1 spot on the Senate ticket will be decided by a ballot of Greens membership. Nominations are open until next week.

The ABC understands that while Senator Hanson-Young won the last closely fought preselection battle, attitudes may be shifting within the party to back another candidate.

Sources within the Greens have alleged Senator Hanson-Young did not help the party during the South Australian election campaign, and was overseas at World Economic Forum events in Davos, Switzerland and Harvard University in the United States.

An image that says “Sarah Hanson-Young, Senator for South Australia” with no reference to the Greens.

Preselection opened last Monday, and closes at the end of this week. A vote of all SA Greens members will follow over April and May.

Earlier this year, the NSW Greens voted to dump senator Lee Rhiannon from top spot on the party’s Senate ticket in favour of state Upper House member Mehreen Faruqi, after a furious dispute with her colleagues which led to her temporary exclusion from the Greens party room.

Preselection battles have also flared in Victoria, as party members face allegations of sabotaging Greens candidate Alex Bhathal’s campaign in the Batman by-election.

Mr Simms, a former Adelaide councillor, was selected by the Greens to replace former senator Penny Wright in a casual vacancy in 2015.

He ran as the Greens’ candidate in the inner-city seat of Adelaide at the state election earlier this month, securing 12.6 per cent of the vote, a marginally better result than his previous attempt at the 2014 state election.

In late 2016, she expressed disappointment at the decision of party leader Richard Di Natale to strip her of the high-profile immigration portfolio.

Speculation over her future in the party was further fuelled last year, when Senator Hanson-Young adopted new branding on her email communications, without reference to the Greens.