A protest march against new sexual discrimination laws will take place outside parliament today, as peers debate a motion to annul the regulations altogether.
Christian and other religious groups are calling on ministers to scrap new legislation that would stop people refusing to provide their goods or services to gay or lesbian people, and will present a 10,000-signature petition to the House of Commons later today.
They fear the law would force bed and breakfast owners to offer double rooms to gay couples even if they believe homosexuality is wrong on religious grounds. Christian printers would also have no right to refuse to print up posters for a gay pride march.
The Northern Ireland Sexual Orientation Regulations came into effect on January 1st, and similar laws are expected to be introduced across the UK by April. However, the House of Lords will tonight debate a motion to annul the existing law before that happens.
"The debate in the Lords is a signal to the government of the need to acknowledge that these regulations do not currently strike the correct balance between two competing rights," said Thomas Cordrey of the Lawyer's Christian Fellowship.
"Christians have no desire to discriminate unjustly on the grounds of sexual orientation, but they cannot and must not be forced to actively condone and promote sexual practices which the Bible teaches are wrong. It is a fundamental matter of freedom of conscience."
Writing in The Daily Telegraph, Lord Mackay of Clashfern, the former Conservative lord chancellor, also argued against the legislation.
"If, as I believe, the regulations are intended to make it unlawful to refuse to facilitate homosexual acts, then it is obvious that those who practise a faith that considers homosexual activity to be sinful are being subjected to a law that seeks to over-ride their consciences," he said.
He added: "The prime minister frequently says we are now engaged in a world-wide struggle for the values we hold dear. The right to respect for the views sincerely held by the individual's conscience is surely one of these."
Campaigners are also mounting a court challenge against the way the regulations became law - they argue the government rushed the consultation.
However, TUC general secretary Brendan Barber warned ministers not to give in to these "religious bigots", arguing that the new regulations would give lesbians and gay men the same rights as every other UK citizen.
"No-one should be denied a room in a hotel or the right to adopt a child simply because of their sexual orientation," he said.
"But this is exactly what some religious leaders believe should happen and they are pressurising the government to continue to allow lesbians and gay men to be treated as second-class citizens."
Labour MP Angela Eagle also defended the laws, saying they were "very sensible and moderate" and gave to lesbians and gay people "exactly the same rights" as other groups have on the grounds of their religious beliefs.
"We are not curtailing religious freedom. People can argue against the practice of homosexuality if they must, but I think it would be more honest for people who are objecting to say that they wanted to abolish all equality law," she told Today.