Five of England's leading letting agents are discriminating against tenants on housing benefit, a report has claimed.
An undercover investigation of 149 regional letting agent branches found one in 10 has a policy not to let to anyone on housing benefit, regardless of whether they can afford the rent.
The report by homelessness charity Shelter and the National Housing Federation said Haart is the worst offender, with mystery shoppers encountering a ban on housing benefit tenants in eight out of 25 branches.
Others named as having individual branch policies not to accept people on housing benefit were Bridgfords (two out of 25 branches visited), Dexters (two out of 25), Fox & Sons (two out of 24) and Your Move (one out of 25).
Almost half (48%) of branches called said they had no suitable homes or landlords willing to let to someone on housing benefit, the report said.
The two housing organisations have joined forces to urge letting agents and landlords to remove bans, which they argue are unfair and "likely to be unlawful".
The report claims that a shortfall in social housing means that an estimated 1.64 million adults rely on housing benefit to help cover private rents.
It said the majority are women, and especially single mothers with childcare responsibilities, while people who receive disability benefits are three times more likely to need a housing benefit top-up.
It said letting agents who reject housing benefit tenants outright could be at risk of breaking the law because of indirect discrimination against women and disabled people.
Shelter chief executive Polly Neate said: "This ugly undercurrent of discrimination is wreaking havoc on hundreds of thousands of people's lives. 'No DSS' is an outdated and outrageous example of blatant prejudice.
"Private renting is now so expensive that many people simply can't get by without some housing benefit, even if they're working.
"At Shelter we hear from families - who've always paid their rent - being pushed to breaking point after having the door repeatedly slammed shut on them just because they need housing benefit.
"Rejecting all housing benefit tenants is morally bankrupt, and because these practices overwhelmingly impact women and disabled people, they could be unlawful.
"That's why we're urging all landlords and letting agents to get rid of housing benefit bans, and treat people fairly on a case by case basis."
David Orr, chief executive of the National Housing Federation - which represents social landlords of around six million people, said: "Letting agents should be ashamed that discrimination is still happening today in the form of an outright ban on people simply because they depend on housing benefit. We know this is purely based on prejudice."
Equality and Human Rights Commission executive director Melanie Field said the body would consider the evidence and deciding whether any action can be taken.
David Cox, chief executive of letting agents' body Arla Propertymark, said: "Rents are paid in advance, whereas housing benefit is paid in arrears, and therefore with such a shortage of rental accommodation, landlords and agents will naturally choose a tenant who can pay the rent when it is due, rather than a tenant who is always a month in arrears.
"We have called on Government time and time again to resolve this problem. But our calls have fallen on deaf ears.
"This situation does not exist because of landlords or letting agents, it is a systemic problem caused by Government and the banks."
A Fox & Sons spokeswoman said: "We can confirm that we certainly do not have a policy to discriminate against tenants in receipt of housing benefits, and our branches are guided to always take instructions from our landlords."
A spokesman for Haart said: "It is not our policy to refuse housing benefit tenants - anyone who passes referencing checks is able to rent properties listed with our branches. We do regularly arrange tenancies for those claiming housing benefits and currently have 112 tenancies where this is the case.
"This research has brought to light that some of our branches are misinformed and we are working to ensure that this policy is being followed across our network. We are sorry for any occasion where this has not been the case."