Police were called to break up a sit-down protest in a central London Tesco store.
Around a dozen Right to Work campaigners forced the Tesco Express branch at Portcullis House - opposite the Houses of Parliament - to close for an hour.
They were demonstrating over a job advert looking for permanent workers in exchange for expenses and jobseeker's allowance. Tesco has amended the "misunderstood" advert and says it was down to a mistake.
The work placement was offered under the Government's "sector-based work academy scheme" which is linked to payment of benefits - but Tesco said the impression that it was seeking to replace full-time workers was mistaken. Placements last for six weeks, the Department of Work and Pensions said.
A spokesman added: "Tesco is one of Britain's leading employers and we know the opportunities they provide are hugely valuable to young people.
"The scheme is voluntary and no one is forced to take part and the threat of losing the benefit only starts once a week has passed on the placement - this was designed to provide certainty to employers and the individuals taking part."
Unions called for high street chains to withdraw from Government programmes.
Tesco has explained that the advert was "a mistake caused by an IT error by Jobcentre Plus" which was being rectified.
The campaigners chanted: "Tesco bosses hear us say, we won't work if you won't pay," and held placards reading, "Tesco. Exploitation. Every little helps."
As many police officers as protesters were sent to break up the small demonstration and no arrests were made.