The largest public sector union may put up candidates to face politicians that it believes are undermining public services.

The annual conference of the Public and Commercial Services Union (PCS), which has no official affiliation, will today discuss a motion calling for it to back candidates who stand against ministers and other MPs.

Examples could include James Purnell who union members have accused of privatising the welfare state.

The move is being supported by the union's leadership and general secretary Mark Serwotka, who has said he would like to see a postal worker stand against Pat McFaddden, the minister leading the part-privatisation of Royal Mail.

But even if the motion is passed, a lengthy consultation period would mean it would not apply to next year's general election, but future contests.

At the same conference, Serwotka branded MPs "disgraceful hypocrites" for cutting services while claiming "obscene" expenses.

If anyone else had made the same kinds of claims or offered the same kinds of excuses as MPs, they would have faced dismissal and possible prosecution, Serwotka said.

"It is important to understand the hypocrisy of all this. These are the same MPs who cheered Gordon Brown when he said he would cut 100,000 civil service jobs," he told delegates.

"Today they are calling for pay restraint while awarding 2.33 per cent for themselves and 1.5 per cent for people battling the recession on the front line."

He added: "They should hang their heads in shame and stop asking us to pay for the mess this country is in while they continue lining their pockets.

"If one of our members claimed expenses for cleaning chandeliers or cleaning a moat and then said that maths wasn't their strong hand, they would be frogmarched out of the building, suspended and then lose their job."

The government was "morally bankrupt", he said, and angrily attacked a recent decision to allow a demonstration by the BNP outside a Home Office site in Croydon which deals with asylum-seekers and immigrants.

"Civil servants have never been so demoralised, never felt so undervalued, while stress levels soar to record levels. In the coming year we will have to fight job cuts, privatisation and market testing."