New rules aimed at banning discrimination by employers, covering areas such as age, disability and pay, have come into force across Britain.
The Equality Act covers many workplace areas and draws nine separate pieces of legislation into a single Act.
Equalities Minister Theresa May says it will now be easier for firms to comply with anti-discrimination rules.
However, some business groups argued the new legislation will impose a heavy burden on employers.
The new laws apply in England, Wales and Scotland, but not Northern Ireland.
The new law restricts the circumstances in which employers can ask job applicants questions about disability or health prior to offering them a position, making it more difficult for disabled people to be unfairly screened out.
"In these challenging economic times it's more important than ever for employers to make the most of all the talent available," said Ms May.
There are also new powers for employment tribunals.
The Act will also stop employers using pay secrecy clauses to prevent employees discussing their own pay, which means men and women can compare pay.
But the Act will not make employers reveal how much they pay men compared with women, as had been planned by the Labour government.
Some campaigners argued that this revision undermined the new legislation.
"Rowing back on the requirement for big business to publish and take action on any differences in pay between men and women employees is tantamount to endorsing the shocking gender pay gap," said Ceri Goddard, chief executive of the Fawcett Society, which campaigns for gender equality.
The Equality and Human Rights Commission said: "Everyone is protected by the new law.
"It [the Act] covers age, disability, gender reassignment, marriage and civil partnership, pregnancy and maternity, race, religion and belief, sex (meaning gender) and sexual orientation.
"Under the act people are not allowed to discriminate, harass or victimise another person because they belong to a group that the Act protects, they are thought to belong to one of those groups or are associated with someone who does."
But some business groups argued that the new rules place an extra burden on companies at a time when they are still trying to recover from the recession.
"Businesses are really concerned," Abigail Morris from the British Chambers of Commerce told the BBC.
"The government's own impact assessment shows that this is going to cost £190m just for businesses to understand the legislation, and this at a time when we really need them to be concentrating on creating private sector jobs and driving economic recovery."
During the summer there were some concerns about the new rules expressed by shipping companies.
Some claimed the laws could force them to quit the UK because they would have to pay UK rates to foreign-based seafarers who do not have the burden of British living costs.