An influential committee is set to query the exemption of religious orders from legislation giving equal rights to gay and lesbian workers.

The joint committee on statutory instruments will demand an explanation for the loophole which allows spiritual organisations to sack employees if the "nature and context" of their job "conflicts with the [strong] religious convictions of a significant number of the religion's followers".

Strong pressure from the Church of England forced the government to make the concession as senior clerics feared the Church would be subject to legal challenges if they refused to ordain homosexuals.

The move comes despite growing calls for the formal entry of members of the lesbian and gay communities into the ranks of the clergy, a campaign which is said to be privately backed by the Archbishop of Canterbury.

Opposition to the clause has centred around the joint committee of peers and MPs, as the legislation will not be subject to debate on the floor of the Commons.

The committee of MPs and peers wants to quiz government officials on the rationale behind the decision.

Gay rights campaigner Peter Tatchell slammed the decision to allow the church to discriminate.

"The government has capitulated to the forces of religious extremism. It has given them the right to veto equality and perpetuate discrimination," he said.

The decision to institute a formal legal right to discriminate was also attacked inside parliament.

Former cabinet minister Chris Smith said: "It is wrong to discriminate in employment whoever the employer may be and that is surely what the law should say."

And the row is unlikely to fade away, with the Lesbian and Gay Christian Movement claiming the move would "make Section 28 look like a tea party".

The DTI accept that the loophole may result in redundancies but said consideration had to paid to religious concerns as well as to bringing Britain in line with the European directive on sexual and religious discrimination.

The department claims that heterosexuality could only be insisted upon in circumstances where it was a "genuine occupational requirement", rather than as a reason to exclude all homosexuals from employment in the church.