More than three million workers are now in "precarious" jobs, often being denied redundancy pay or protection from unfair dismissal, a study reveals.
Research by the TUC showed that one in 10 people were employed in the so-called "gig" economy following an "explosion" of insecure work.
The number of workers denied employment protection has doubled in the past decade to 1.5 million, said the union organisation.
Its report, Living On the Edge, showed that workers on controversial zero hours contracts earn £3.80 an hour less than average employees, while the self-employed and casual staff earn 40% less.
Almost half a million workers have no legal right to sick pay because their earnings are so low, said the TUC.
General Secretary Frances O'Grady said: "Insecure work has exploded in the past decade. In far too many cases, the only people who've benefited are bad bosses. Sports Direct can't be the employment model for the 2020s.
"Gig economy workers face the double hit of poverty wages and weaker employment rights. Whether they're waiting tables or driving for Uber, all workers deserve respect, fair pay and basic protections.
"But the law hasn't kept pace with how work has changed. That's why the Taylor review must drag the rules that protect working people into the 21st century."
The TUC said the current review of employment practices being undertaken for the government should recommend strengthening legal protections for precarious workers.
A Business Department spokesman said: "We are keen to ensure our employment rules keep up to date to reflect new ways of working, and that's why the Government has asked Matthew Taylor to conduct an independent review into modern working practices."