Another 11,000 people are receiving letters from HM Revenue and Customs (HMRC) questioning claims for self-employment support grants.
The UK’s tax authority sent 24,000 similar letters last year to claimants who said they had stopped trading.
The Coronavirus Self-Employed Income Support Scheme (SEISS) has paid three grants so far during the crisis.
A total of £18.5bn has been paid to those whose businesses have been affected.
Other self-employed people have said they have been excluded from the same financial support.
HMRC has sent letters to people who said they had ceased trading either on their 2019-2020 self-assessment return or by amending their return for the previous year.
They were sent to people who had told HMRC that, at some point, they had stopped trading, and so would only be eligible if they had restarted.
“If they claimed correctly, we may ask them for extra documentation to show this. If they were not eligible, they will have to repay the relevant grants,” a spokesman for HMRC said.
“Anyone found to have knowingly claimed a grant they were not eligible for could face a financial penalty.”
Those who do not reply to the message within 21 days would not be allowed to apply for future SEISS grants until they made contact with HMRC, he added.