Charities are calling on the chancellor to protect the jobs of workers who have been shielding during the pandemic.
A total of 15 charities have warned in an open letter that workers will be forced to choose between health and their jobs, when restrictions ease.
"Some of these workers will find themselves in an impossible position," the letter says.
A government spokesperson said that the government had "worked tirelessly" to support the clinically vulnerable.
From 1 August, extremely clinically vulnerable people who have stayed at home to protect themselves from coronavirus in England, Scotland and Northern Ireland are allowed to return to work.
But charities including Age UK and Macmillan Cancer Support have said that these employees could be at risk of being made redundant, or returning to the workplace when they do not feel it is safe.
More than two million people deemed extremely vulnerable to coronavirus are shielding in England. About 595,000 of those people usually work, according to the charities.
"Our concern is that, especially as your furlough arrangements start to unwind and the shielding scheme is paused from next week, some of these workers will find themselves in an impossible position," the charities write in the letter.
"This is because if their occupation is one which they cannot carry out from home, and if it is extremely difficult to make their workplace safe for them, they may be forced to choose between putting their health on the line by returning, or staying safe by giving up their job."
The charities say this is "desperately unfair" for those who have made "great sacrifices" by staying at home, and call on Chancellor Rishi Sunak to take action and protect their jobs, as well as supporting businesses.
A spokesman for the Treasury said: "We understand how challenging the outbreak pandemic has been for the clinically vulnerable and we have worked tirelessly to support them.
"Employers must ensure the safety of those with such conditions when considering working arrangements, including whether work can be completed remotely."
He added that the Treasury had also announced £750m in funding for charities to enable them to continue their important work, ensuring those on the front line are able to reach people who need help.
Chris Askew, chief executive of Diabetes UK and a signatory of the letter, said: "No-one should be faced with the impossible task of choosing between their health, by returning to work in an unsafe environment, and their financial security.
"The government must ensure that employers are supported to take all the necessary measures to keep all employees safe, if they are expected to attend work outside their home.
He added that the government should introduce a new support scheme for clinically vulnerable people who are unable to return to a safe work environment.
Employers have been told to make sure that people who are shielding can work from home wherever possible, including moving them to another role if required, according to government guidance.
If bosses cannot provide a safe working environment, those who are clinically vulnerable will be able to access financial support including statutory sick pay and welfare payments, it has said.
The charities' letter also suggests extending the furlough scheme for those who have been shielding or are at high-risk.
Currently, the UK's coronavirus furlough scheme is set to finish at the end of October.
The latest figures show that 9.5 million people are using the scheme, at a total cost of £31.7bn to the Treasury.
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