The Government has introduced new equality rights which ministers say will help stamp out pay discrimination.
Most provisions of the Equality Act come into force from Friday, including a measure to stop pay secrecy clauses being used to hide unfair differences between what men and women are paid.
Around 90% of the Act is introduced on Friday, making the law simpler by bringing together nine pieces of legislation under a single banner.
The Government said it will announce in due course its plans for the remaining parts of the Act.
The change in the law coincides with the release of Made in Dagenham, a British film about women workers at the Ford assembly plant in East London who launched a campaign in 1968 to demand equal pay. Their actions led to the creation of the 1970 Equal Pay Act.
Home Secretary and Minister for Women and Equality Theresa May, who recently met four of the original strikers, said: "Thanks to pioneers like the women who feature in Made in Dagenham, the workplace is much fairer than it was in 1968, but there is still plenty of room for improvement.
"In these challenging economic times it's more important than ever for employers to make the most of all the talent available. When a company reflects the society it serves, it's better for the employer, the employees and the customers, so being a woman should never be a barrier to being treated fairly at work.
"From today the gagging clauses that stop people discussing their pay with their colleagues will be unenforceable, allowing women and men to find out if they're being paid unfairly.
"This move towards transparency is just one part of the Equality Act, which also makes it easier for businesses to comply with discrimination law by streamlining the equality laws, and provides more protection to disabled people."
Other changes coming into force on Friday include extra protection for disabled people and new powers for employment tribunals.