The European Parliament has approved new EU rules to protect workers in the so-called "gig economy".
The law sets minimum rights and demands increased transparency for those in "on-demand" jobs, such as at Uber or Deliveroo.
It proposes more predictable hours and compensation for cancelled work, and an end to "abusive practices" around casual contracts.
Member states will now have at most three years to enforce the new rules.
The European Parliament says the new legislation will apply to "the most vulnerable employees on atypical contracts and in non-standard jobs" - including those on zero-hour contracts.
Employees in EU member states already enjoy a wide range of protections to working hours, minimum breaks and holiday entitlement.
But casual employees in the "gig economy" - who may work multiple jobs on a flexible basis, or on erratic hours - have fallen into a grey area.
The UK will only be obliged to implement the law if it is still a member state of the EU three years after the new regulation enters into force. But it has already introduced similar legislation at a national level.
The EU law will require employers to inform all workers about "essential aspects" of their employment on their first day, including:
- Description of their duties
- Starting date and pay information
- Indication of what a standard working day is, or reference hours
- Right to compensation for late cancelling of work
- Only one probationary period, lasting a maximum of six months
- Allow employees to have other jobs, banning "exclusivity clauses"
The new rules should apply to all those who work at least three hours a week, averaged over four weeks - at least three million people, though it is a growing category of workers.
The rules will also apply to trainees and apprentices in similar circumstances.
Enrique Calvet Chambon, the MEP responsible for seeing the law through, said it was the first EU legislation setting minimum workers' rights in 20 years.
"All workers who have been in limbo will now be granted minimum rights thanks to this directive... from now on no employer will be able to abuse the flexibility in the labour market," he said.
EU officials say the new rules will not apply to "genuinely self-employed" people who work for themselves.