The TUC annual congress, which begins in Brighton on Monday, includes a motion calling for proposed new equality duties for public bodies to be extended to the private and voluntary sectors.
The Government is proposing that the current duty for public bodies to promote race, disability and gender equality be extended to cover sexual orientation, gender reassignment, age and religion or belief. The changes are expected in the forthcoming Equality Bill.
The motion, submitted by civil servants union the First Division Association, says the TUC should lobby the Government to apply the new duties to the private and voluntary sectors as well.
If the Government agrees, charities will be compelled to write equality schemes, consult with different groups when designing services, monitor their impact and ensure that negative effects on equality are addressed.
Sarah Brett, equality policy officer at the TUC, said that if the single equality duty was not applied across the economy there would be "two-tier legislation", with high standards for the public sector and less stringent rules for other organisations.
"At a minimum we think that the equality duty should directly apply to voluntary organisations that deliver public services or carry out a public function," she said.
Kate Jopling, head of public policy at Help the Aged, said that promoting equality was second nature for many voluntary organisations, but the charity was not opposed to extending the equality duty to the sector.
"We wouldn't support anything that would be a heavy bureaucratic burden for small organisations," she said. "For the big government departments there are some quite bureaucratic processes around this. The idea is that it will be light-touch and flexible."
A spokeswoman for the Government's Equalities Unit said it had no plans to extend coverage to the voluntary sector. "The general duty will cover private sector or voluntary bodies that are carrying out public functions on behalf of and under contract to public authorities, but only with regard to those functions," she said.
She added that the Government was exploring other ways to achieve transparency on equality for organisations outside the public sector, including a kitemark scheme.
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