Plibersek tries to stem tide to Greens

As the Labor Party bleeds support to the Greens, deputy leader Tanya Plibersek is set to make a pitch to progressive voters.

Ms Plibersek says the upwards trajectory of the Greens might not last as she prepares to deliver a keynote speech to the McKell Institute in Sydney on Wednesday.

"We've seen parties like the Democrats come and go ... I don't think you can say this is a determined long-term trend," she told ABC Radio.