Comic actor Rowan Atkinson and former Archbishop of Canterbury Lord Carey joined forces with a cross-party group of peers to propose new safeguards.
They say the government will not scrap the planned legislation and so are demanding changes.
Ministers reject claims that the current bill would stop free speech.
The Racial and Religious Hatred Bill faces detailed scrutiny when it has its committee stage in the House of Lords next week.
Current race hate laws cover Jews and Sikhs but the government says people from other religions, such as Muslims, need protection.
Opponents of the bill, which faces detailed scrutiny in the House of Lords next week, say it would outlaw jokes and criticism of beliefs.
They argue that people can choose their religion, unlike their race and so should not be protected against offence or criticism.
On Thursday, the alliance of writers, comedians, bishops and peers unveiled a series of amendments they want added to the bill.
They want three safeguards would ensure the bill protects people, rather than beliefs.
The proposed safeguards are:
Nobody can be found guilty of new religious hate crimes unless it is proved they intended to stir up hatred
Only threatening words should be banned by the bill, not those which are only abusive or insulting
There should be a specific part of the bill saying the law should not restrict discussion, criticism of expressions of antipathy, dislike, ridicule, insult or abuse of particular religions or beliefs.
Liberal Democrat peer Lord Lester said: “The purpose of these amendments is to take the rot out of a rotten bill.”
He said ministers were unlikely now to scrap a bill which they had promised both in Labour’s manifesto and in a pre-election letter to every mosque.
“We think it would be a mistake to wreck the bill and then give the government the excuse that the unelected upper house was somehow thwarted the will of the elected representatives,” he said.
Witches and elections?
Blackadder star Mr Atkinson said campaigners against the law backed the government’s alleged intentions.
But he warned: “The prime motivating energy for the bill seemed to come not from communities seeking protection from bullying by the British National Party but more from individuals with a more aggressive, fundamentalist agenda.”
He pointed to those who would have liked to use such laws to prevent Salman Rushdie’s Satanic Verses.
Even if there were no prosecutions under the new law, it would create self-censorship by writers, suggested Mr Atkinson.
The government has said there would not be “frivolous” cases under the new law because every prosecution would have to be approved by the attorney general.
Mr Atkinson said there had been attempts in America to use similar laws against Christians for vilifying witches.
He joked that the attorney general, as a member of the government, might not think such cases were frivolous if there was a surprising number of witches who could swing the election in key marginal constituencies.
Lord Carey said the changes were designed to help the government protect people from religious minorities while keeping free speech.
“It is good for religions to be knocked, to be challenged because we have done a lot of damage in the past,” he said.
Bad jokes could be very offensive but the aim should be to create a society where people were sensitive to the feelings of others, he argued.
A Home Office spokesman said: “We have seen and will consider the proposals and respond to them in due course.”