Leading addiction charities have expressed deep concerns over government plans to cut the benefits of people suspected of suffering from alcoholism or drug addiction who refuse treatment for their condition.

In a sign of the government's new benefits regime – which lies at the heart of Iain Duncan Smith's cost-cutting welfare changes – staff in Jobcentre Plus offices will be encouraged to cut the jobseeker's allowance of claimants who reject treatment for addiction.

The new rules will come into place in October 2013, when the universal credit, which is designed to wrap benefits into one payment, is introduced.

A new claimant contract lies at the heart of the universal credit reforms. Claimants will have to sign a contract in which they agree to look for work in exchange for an undertaking from the government to support them while they do so.

Government sources said the contract would allow Jobcentre Plus staff to say that suspected addicts were in breach of their commitments if they refused help for alcoholism or drug addiction.

However, some of those involved in helping people addicted to drugs and alcohol warn that removing benefits could jeopardise their recovery.

Niamh Eastwood, the chief executive of the charity Release, said: "Iain Duncan Smith's proposal is tantamount to coercive treatment. The previous government attempted to introduce mandatory treatment through their welfare reforms of 2009. The clause was dropped in the final hours before the legislation was approved because of concerns over legality.

"There are similar concerns around what is being proposed by the secretary of state for the Department for Work and Pensions today. In no other area of health would we see such an approach being taken, but again and again successive governments seek to stigmatise further those with addiction who are often vulnerable and marginalised individuals and fail to recognise the complex nature of this condition."

Eastwood said she was concerned that at no time during the parliamentary passage of the welfare reform bill was it proposed that the claimant contract would include a "treatment or sanctions requirement". Without proper scrutiny of the proposal this should not go through, she said.

Martin Barnes, the chief executive of DrugScope, has written to the work and pensions secretary asking him to clarify the plans.

"We are surprised and concerned at reports that ministers believe that stopping benefits is an appropriate or effective way of engaging people with drug or alcohol treatment and supporting their recovery," he said. "If accurate, this would be a reversal of the government's publicly stated position."

Barnes said there was no evidence to suggest that "using the stick of benefit sanctions" would help people engage with treatment and aid recovery.

He added: "Indeed, the risk is that people will disengage from support services, potentially worsening their dependency and the impacts on their families and communities. Linking benefit to a requirement to undergo treatment would set a dangerous precedent for people with physical or mental health problems and would be against the principles for healthcare set out in the NHS Constitution."

Barnes said that while DrugScope welcomed the government's commitment to supporting people in treatment and recovery, "much more needs to be done to make this a reality".

Simon Antrobus, the chief executive of Addaction – one of the UK's largest specialist drug and alcohol treatment charities – said people could not be forced into abstinence.

"Encouraging people with serious drug and alcohol problems to access support is always the best option," he said.

"Those that Addaction help on a daily basis will tell you how coming off drugs or alcohol is extremely difficult, and how deciding to access treatment took them a very long time. Remove financial stability during that time, and you can severely damage someone's chances of beating an addiction and recovering."

Antrobus said family-focused, properly funded and integrated community treatments would prove far more effective, adding: "The jobcentre could prove to be an excellent referral to that kind of support, without resorting to measures that could only add to a person's problems."

That view was echoed by Eric Appleby, the chief executive of Alcohol Concern.

"Incentives are only part of the story; the real answer is to make sure that high quality treatment services are fully funded and available all over the country," he said.

"At the moment only one in 16 people with an alcohol problem are receiving specialist alcohol treatment. In order to make this work, jobcentre staff will need to be properly trained in order to recognise when someone has an alcohol problem and to be able to offer the right advice."

Sir Ian Gilmore, the Royal College of Physicians special adviser on alcohol, said: "Current treatment facilities for addicts in this country, particularly those with alcohol dependence, are woefully inadequate and we strongly support initiatives to improve this. However, patients must be treated with respect and given genuine choice in their treatment options, and these must be fully respected in any scheme."

Duncan Smith will give a sense of the new rules when he addresses an event in parliament organised by Alcoholics Anonymous on Wednesday.

He will say: "The outdated benefits system fails to get people off drugs and put their lives on track. We have started changing how addicts are supported, but we must go further to actively take on the devastation that drugs and alcohol can cause.

"Under universal credit we want to do more to encourage and support claimants into rehabilitation for addiction and starting them on the road to recovery and eventually work. Getting people into work and encouraging independence is our ultimate goal. Universal credit will put people on a journey towards a sustainable recovery so they are better placed to look for work in future and we will be outlining our plans shortly."

It is understood that the work and pensions secretary will not make a formal announcement on Wednesday of the powers that will be handed to Jobcentre Plus staff, but a government source said Duncan Smith believed it was right to give them powers to cut benefits if an addict refused treatment because they could detect signs of trouble.

The source said: "The universal credit will allow staff in Jobcentre Plus offices to say: this person has been unemployed for some time. The staff know if people are addicted to alcohol. They know the people they are dealing with.

"But we want this to be positive and to be about signposting people to superb organisations that can help them. This is about changing their lives. It is very important to support addicts into the workplace."

But if claimants refuse they will have their benefits docked. "There will be sanctions," the source said, citing cuts to the jobseeker's allowance as an example.