The UK is at a "real risk" of falling behind the EU when it comes to workers' rights, the Trade Union Congress (TUC) says.
The union body said the EU had "various initiatives" in the pipeline which would improve standards once they became law.
But it said the UK had no similar legislation on the way.
The government said in protecting workers' rights the UK already "goes further than the EU in many areas".
The TUC's call comes three months after a new post-Brexit trade deal came into force between the UK and EU.
Both sides have committed not to lower labour standards in a way that impacts trade or investment - but that does not mean they have to match each other.
Nonetheless, the TUC said the UK had already failed to implement directives it agreed to while still a member of the EU, including:
- A work-life balance directive, which gives fathers the right to day-one paid paternity leave and gives all workers the right to request flexible work
- And a transparent and predictable working conditions directive, which gives workers compensation for cancelled shifts, predictability of hours for zero hours contracts, and a right to free mandatory training.
It said further initiatives were being considered by the EU that could improve conditions for "platform workers" and give employees the right to "digitally disconnect" outside working hours.
The bloc is also looking at ways to make employers accountable for the rights of workers in their supply chains.
TUC general secretary Frances O'Grady said that "as a bare minimum, the government must keep the pace with the EU on rights".
"Just three months after the UK-EU deal came into force, we're already at real risk of losing ground to the EU on workers' rights.
"Again and again, Boris Johnson promised that his government would protect and enhance workers' rights. It's high time the prime minister lived up to his word."
A spokesperson from the Department for Business, Energy and Industrial Strategy (BEIS) said the UK offered workers "generous holiday pay and high standards for workplace safety".
BEIS cited as examples that the UK annual leave entitlement of 5.6 weeks compared favourably with the four weeks required in the EU. The UK allows parents to share paid parental leave, which the EU does not, BEIS said. It also said the UK had one of the highest minimum wage rates in Europe.
"We have a strong record of protecting and enhancing workers' rights and are committed to going further to make the UK the best place in the world to work," the spokesperson said.
However, Ms O'Grady noted the government had promised to introduce a new employment bill to improve people's rights at work in 2019 but was yet to bring it before Parliament.
She said the bill could "end exploitative work practices like zero-hours contracts, once and for all".
In January, Business Secretary Kwasi Kwarteng scrapped a planned review of workers' rights amid fears it would lead to an erosion of job protections, such as the 48-hour week, holiday entitlements and overtime pay.
At the time, Mr Kwarteng stressed the government had never intended to water down standards and if anything wanted to raise them.
The government said an employment bill designed to enhance workers' rights would be brought forward "when parliamentary time allows".