Citizens Advice found workers who are shielding at home have, on average, lost £1,400 since the start of lockdown.
The consumer group found many are now struggling with bills and basic living costs.
Citizens Advice found more than one in five (22%) of those who are shielding have fallen behind on a bill.
Of the employment cases they have looked at, 70% involved people not on the government's furlough scheme, which protects employees incomes.
Jess Harris is shielding because she is vulnerable after transplant surgery.
Initially, she was told she’d need unpaid leave to stay off work. Her bosses did find a way for her to work from home - but not before she'd been through days of worry.
She told ITV News: “How am I going to afford food, how do I afford my rent if I’m going to take weeks off work that are not been paid at all?"
What makes things worse is that many who are shielding, is that living expenses can significantly rise for those largely confined to their homes.
Ms Harris said: “My heating has probably been on a lot more, my lights for working have been on the whole time. my laptop has been on the whole time".
Most people who are shielding rely on food deliveries – so no longer have the option of roaming the bargain shelves.
Official guidelines say the most vulnerable should shield - but the government doesn't say employers must put them on the furlough scheme to protect their incomes.
One administration worker spoke to us anonymously after her bosses told her shielding was just a personal choice and that she’d have to return to work or lose her income.
She told ITV News: “I was told shielding was a choice and it was OK for me to go back to work. They said our understanding is that you have to come back in - or go off sick. I very nearly said, 'are you asking me to choose work over staying safe?'”
The government told ITV News that statutory sick pay is available as a safety net for those who are vulnerable and off work.