Tesco has been told not to illegally block rival supermarkets from buying their land or leasing nearby sites.
A competition investigation found the UK’s biggest supermarket chain stopped access 23 times around the UK using restrictive contracts.
Tesco has agreed to take action to avoid this in the future.
The supermarket giant blamed “administrative errors” and said it had strengthened its “controls and training.”
The Competition and Markets Authority (CMA) investigation discovered that in three of the cases, when Tesco was selling land, it had put in place so-called restrictive covenants to stop rivals such as other big supermarket chains buying it, which is illegal.
In 20 of the cases, when Tesco was leasing property from landlords, it would stipulate in the contract that rivals could not also lease in the same building or site for 20 years or longer.
Companies are allowed to make such demands from landlords, but only for up to five years.
Andrea Gomes da Silva, the executive director of markets and mergers at the CMA, said in a statement: “It’s unacceptable that Tesco had these unlawful restrictions in place for up to a decade.
“By making it harder for other supermarkets to open stores next to its branches, shoppers could have lost out.”
The CMA originally found one breach of the rules, and then a review by Tesco found the other 22 breaches, the authority said in a letter to Tesco chief executive Dave Lewis.
“I recognise that Tesco has acknowledged the breaches that have occurred, has cooperated with the CMA in taking forward its analysis and has begun to take remedial action,” Ms Gomes da Silva said in the letter.
“However, in my view, this episode highlights significant shortcomings in compliance for a company of Tesco’s scale and resources.”
Tesco said that it did not use restrictive property agreements, but that “in a small number of historic cases between 2010 and 2015, administrative errors by former advisors meant that our internal processes were not followed correctly.”
“As the CMA recognises, we have worked collaboratively in resolving this, and our voluntary review of 5,354 land deals found isolated issues in just 0.4% of these,” it said in a statement.
“We have since strengthened our controls and training,” and it will drop the offending contract terms, it said.