The town's infection rate had rocketed to 464 per 100,000 of population as of Friday.
Current Covid regulations state that people should stay at home other than for specific purposes.
And strict national restrictions mean non-essential retail should be closed other than in specific circumstances.
Middlesbrough Council's Public Protection team is investigating several potential breaches of the regulations covering businesses.
Only essential retail such as food shops, supermarkets, pharmacies, garden centres, hardware stores and off-licences should be open.
Non-essential retail, such as clothing and homeware stores and shops selling electronic goods and mobile phones should be closed other than for click-and-collect.
Middlesbrough Mayor Andy Preston said: ""We all want life to return to normal as soon as possible. That will only happen when we get Covid under control. Anyone ignoring the restrictions puts our plans for the future on hold."
"Most people and business around Middlesbrough are doing the right thing when it comes to Covid.
"They are understandably fed up of seeing examples of those who ignore the rules and put others at risk.
"Council staff are working flat out to make businesses aware of the regulations. We will come down hard on those that don't follow what is a very clear message."
National restrictions are due to end on December 2 but the government has indicated the tiered approach to lockdown rules will return after that date.
If Middlesbrough's infection rate remains high, it's likely the town will remain subject to strict conditions that would have a negative impact on businesses and families over the Christmas period.
The Council has a dedicated Covid regulations team that is working to educate businesses on the restrictions.
Visits and test purchases will continue over the weekend with a number of fixed penalty notices already issued.
The Council's street wardens are also carrying out Covid marshalling duties and can call on the support of Cleveland Police to deal with breaches of the regulations.