The government has launched a £1m campaign to help employment agencies understand the law about their workers.
The campaign will also use posters, the internet and local press to encourage workers to be aware of their rights.
Business Minister Pat McFadden will write to more than 13,000 employment agencies to outline how they can make sure they are complying with the law.
The government is responding to union concerns that agency workers are being cheated of their rights.
TUC General Secretary Brendan Barber said: “Of course most agencies act within the law, but some agency workers miss out on the most basic employment rights, and are among the most vulnerable in the whole workforce.
“This is why we welcome the government’s plans to make sure agency workers know their rights and to ensure more effective enforcement of their rights.”
Minister for employment relations Pat McFadden said: “Employment agencies need to make sure they play by the rules and don’t short-change their staff.
“An economic downturn should not be an excuse to deny people their rights to work.
“This campaign will help agency workers know their rights and help employers know their responsibilities.”
The Employment Agency Standards inspectorate, which recently doubled in size and extended its investigative powers, will also work along side the government on this campaign.
Katja Hall, director of employment policy at the CBI, welcomed the government campaign.
“Increasing people’s knowledge is an important first step in ensuring that workers access the rights to which they are entitled,” she said.
In April 2008, the Conduct of Employment Agencies and Employment Businesses (Amendment) Regulations 2007 came into force, partly to protect agency workers.