Ministers could face an unlimited fine if they are found to have broken the law in their treatment of disabled people after a watchdog launched the first investigation of its kind into a government department.
The probe, by the Equality and Human Rights Commission, follows the deaths of a number of vulnerable benefits claimants.
Baroness Kishwer Falkner, the chair of the EHRC, said her organisation was “extremely worried” about the treatment of some disabled people by the Department for Work and Pensions. “We suspect the Secretary of State's department may have broken equality law,” she added.
She described the investigation as the “strongest possible action” they could take.
Whistleblowers who have worked for the DWP and disability charities have been asked to be in touch.
The regulator began looking into the department after a group of MPs recommended it investigate the deaths of vulnerable claimants, by suicide and other causes, between 2008 and 2020.
The EHRC is looking at whether the DWP failed to make reasonable adjustments for those with learning disabilities or long-term mental health conditions during assessments for some benefit payments.
Baroness Falkner said the department was responsible for “vital support which many disabled people rely on… access to that support must be fair.”
"Our investigation… will find out whether the DWP and the Secretary of State have breached equality law. If they have, we will use our unique legal powers to hold them to account."
Possible sanctions are understood to include an unlimited fine.
The watchdog can also take the department to court if it does not co-operate with its probe. It is thought to be the first time the EHRC has used these powers to investigate a government department.
Work and pensions secretary Mel Stride has previously been criticised after he said people with depression or anxiety could lose access to sickness benefits under planned reforms.
On Tuesday he claimed changes to the welfare system would uncover hidden “treasure” in the talents of unemployed Brits, unveiling “skills bootcamps” designed to cut reliance on overseas workers.
The UK had depended on foreign labour "for too long", he said, as he announced those on benefits would be offered training for roles in key sectors such as hospitality, care and construction.
The EHRC previously investigated Labour and found it had broken the law for its handling of antisemitism under former leader Jeremy Corbyn.
A damning report, published in October 2020, found “inexcusable” failures which “appeared to be a result of a lack of willingness to tackle antisemitism rather than an inability to do so”.
It demanded a series of changes and continued to monitor the party for more than two years.
Mr Corbyn was also kicked out of the parliamentary party and remains an independent MP after he said he did not accept all of the EHRC findings.
David Linden MP, the SNP's social justice spokesperson, accused the DWP of “failing disabled people for decades", and said "full transparency and accountability is imperative".
The DWP and Mr Stride have been contacted for comment.