Scottish Labour leadership hopeful Neil Findlay has secured the support of train drivers trade union ASLEF.
Mick Whelan, the organisation’s general secretary, said the Lothians MSP had the “character, vision, talent and ability” to deliver change for society.
Mr Finday, a former bricklayer, housing officer and English teacher who was first elected to Holyrood in 2011, has vowed to return the party to its left-leaning socialist values.
He has promised to put social justice at the heart of everything Labour does to try to “create a fairer, more equal and prosperous Scotland”.
Mr Whelan said he hoped Mr Findlay would be elected first minister in 2016.
“Neil understands what Labour has to do to win back the hearts, the minds, and the votes of working men and women in Scotland,” said the union official.
East Renfrewshire MP Jim Murphy and Lothians MSP Sarah Boyack are also hoping to succeed Johann Lamont as party leader.