Workers have filed 1,868 claims that firms are fraudulently taking furlough money from the government.
HMRC said it has seen the number of furlough fraud reports jump sharply in the period to May 29, having received 795 claims by May 12.
It said it will now be assessing these reports and deciding on the next steps.
The Coronavirus Job Retention Scheme (CJRS) was introduced by the government in March, in a bid to protect jobs.
The scheme will continue to run until the end of October, with 80 percent of furloughed workers’ wages paid by government until September, when the contributions will reduce. Read more about the changes to CJRS here.
An HMRC spokesperson said: “We’d ask anyone concerned their employer might be abusing the scheme to please contact us. It could be that you’re not being paid what you’re entitled to, they might be asking you to work while you’re on furlough, or they may have claimed for times when you were working.
“We won’t hesitate to take criminal action against the most serious cases.”
HMRC said the claims are checked and furlough payments may be withheld or need to be repaid if the claims are revealed to be based on dishonest or inaccurate information.
If you would like to report furlough fraud, you can do so here.