Opposition Leader Bill Shorten sought to fire up Labor’s trade union base on Sunday, in a fiery speech to the party faithful that portrayed Australia as an increasingly economically-divided society after five years of Coalition government.

And Mr Shorten says Labor is ready to take on the Turnbull government at the 'super Saturday' of five federal byelections across Australia on July 28, scheduled to clash with the national Labor conference.

Mr Shorten blasted the timing of the byelections, which has forced Labor to reschedule its national conference but said ‘‘our business now is byelections’’.

In a room at the Moonee Valley racecourse with up to 700 Labor members present, hundreds of whom wore trade union-branded clothing, Mr Shorten argued that ordinary Australian workers had missed out on recent economic growth because of the Abbott and Turnbull governments' attempts to weaken unions.

“The reason why this government is so obsessed with trade unions is they understand that when you have relentless attacks on unions, you actually see lower wage outcomes for working Australians and the last five years most certainly proves that point,” Mr Shorten said.