Many trade apprentices are living below the poverty line, the Electrical Trades Union says.
Apprentice wages have also failed to recognise that more than a quarter of those entering trades now are aged over 25, the ETU says.
ETU assistant national secretary Allen Hicks said that with first year apprentices now earning barely over half the pay of "an unskilled burger-flipper", it was no surprise that completion rates were critically low.
"The current system is from the 1950s, when apprentices were 15 years old and lived at home with mum and dad," Mr Hicks said.
"It has failed to address the fact that many people who want to enter trades in 2013 are aged in their 20s and 30s, and often have children and mortgages.
"The system also ignores the fact that many modern apprentices are independent adults who start their trade having completed year 12 and even holding vocational education and training qualifications."
A report on the matter, by Workplace Research Centre at the School of Business at the University of Sydney, will be released this morning.