New tighter laws on workplace discrimination come into force this week, in a move welcomed by labour activists but seen as problematic by legal experts.
Sexuality discrimination is now on the same footing as sex bias
On Monday, it becomes illegal to discriminate against workers on grounds of sexual orientation.
On Tuesday, the same strictures are applied to religion.
The development brings these types of discrimination into line with existing practice on sex and race bias.
The Trades Union Congress said it represented a "massive leap" towards fair treatment for gay, lesbian and bisexual workers.
The new laws aim to give workers rights against bullying or exclusion from employee benefits, training and promotion opportunities on grounds of religion or sexuality.
They have the support of the government and unions, and have been broadly welcomed by employers.
But while there have been few complaints about the thrust of the legislation, some lawyers have expressed concern about the complications it might produce.
Unlike race or sex, defining religion is legally problematic, and demonstrating links between workplace behaviour and religion is unlikely to be easy.
Employers, meanwhile, have become concerned that they might become embroiled in a mass of frivolous or concocted complaints from their staff.
And specialist insurer Hiscox warns firms could find themselves at the receiving end of complaints as a result of employees misbehaving at Christmas parties.
Underwriter Angela Howe said: "Discrimination claims can be made against companies even if the (inappropriate sexual) remarks were made outside of the office and outside of working hours.
"This can include sexual remarks made in the pub after work or at a Christmas party."
Figures released on Monday by specialist journal Equal Opportunities Review showed that UK firms were forced to pay out £6.4m in relation to discrimination claims in 2002, up by two-thirds year on year.
Must try harder
The latest developments complement a general tightening of workplace legislation under the Labour government.
Existing sex and race discrimination rules have been broadened, and now cover an employee even after he or she leaves a post.
Stephanie Slanickova, employment lawyer at Tarlo Lyons, said: "I think it will have an substantial impact, and will affect the way in which people go about their everyday lives in the workplace."
Unions say more progress needs to be made, notably in bolstering the rights of same-sex partners, an issue the government has resisted.
Legal experts say the onus is now on employers to review their existing practices - something that may entail a great deal of fact-finding, especially in abstruse areas of religious belief.
Rules on religion could have particular implications in issues such as workplace catering and holiday entitlement, not areas that are generally considered under existing anti-discrimination rules.