Every employer in the country should sign up to the Skills Pledge, the government has stated.
According to David Lammy, joining the initiative will help UK workers obtain world-class skills.
He said: "Every employee has the potential to contribute to business performance and improve standards of customer service, but this potential can only be unlocked if every employee can access high-quality training."
Mr Lammy was speaking after Transport for London gave its commitment to the scheme, an event which means more than four million people are now covered by the agreement.
The Skills Pledge is a voluntary commitment by the managers of a firm to support all its workers to strive towards a Level 2 qualification, the equivalent of five good GCSEs.
Meanwhile the Federation of Small Businesses has urged the government not to cut funding for the Local Authority Business Growth Incentive, which aims to help councils promote business growth.
