Union officials have voiced scepticism that Anthony Albanese can win the next election for Labor, with many having wanted Tanya Plibersek to run.

Heavyweights within the Construction, Forestry, Maritime, Mining and Energy Union, including national secretary Michael O'Connor and Victorian secretary John Setka, were understood to be personally favouring Plibersek over Albanese before she dropped out.

Officials within the Maritime Union of Australia, including national president Chris Cain, had also been considering backing Plibersek while sources said CFMEU mining head Tony Maher would back Albanese.

One influential left-wing union leader praised Plibersek as a stand-out performer who could resonate with both workers and chief executives.

"I think she had that 'Bob Hawke consensus' [quality] about her where she can relate to seven out of 10 people."