Eight Northern Ireland supermarkets are to be given five years to end agreements with landowners which prevent rivals from setting up shop nearby.
In 2008 the Competition Commission proposed changes to planning laws to give local shoppers a wider choice, following a two-year investigation.
A government consultation into the report was carried out, and legislation due to come into effect next April gives supermarket chains a deadline to lift exclusivity arrangements.
The plans, which affect some Asda, Sainsbury's and Tesco stores operating in Northern Ireland, do not require the supermarkets to sell land or shops.
Under the exclusivity arrangements, landowners agreed with supermarkets to either stop other grocery retailers from opening on the same site or limit the sale of groceries by rivals there.
The Competition Commission highlighted eight stores in Northern Ireland operating under arrangements "which prevent, restrict or distort competition":
- Asda in Downpatrick: exclusivity arrangement granted by J and H Miskelly;
- Sainsbury's, Newry: exclusivity arrangement granted by Parker Green;
- Sainsbury's, Ballymena: exclusivity arrangement granted by Sam Morrison, incorporating Braidwater Retail Park and any extension;
- Sainsbury's, Armagh: exclusivity arrangement granted by Drumragh Property Investments on site in The Mall shopping centre;
- Tesco, Portadown: exclusivity arrangement granted by Turret Investments in Meadows Centre;
- Tesco, Newtownabbey: exclusivity arrangement granted by Abbey Retail Park Limited;
- Tesco, Limavady: exclusivity arrangement granted by Sean Mullan and Son on land adjacent to Lower Main Street in the town;
- Tesco, Cookstown: exclusivity arrangement granted by Norman Menary on Orritor Road site.
Among the criteria used by the Competition Commission was whether other large or mid-sized grocery retailers were within 10 minutes' drive.
Competition Commission spokesman Rory Taylor said exclusivity agreements were acceptable when an outlet first opened.
"If you're setting up a new shopping centre, you'd be keen to have a grocery retailer there but the supermarket would not want to see a rival moving in shortly afterwards," he said.
"However, we felt it wasn't justifiable to keep that in place forever, and that is why we suggested putting in a time limit."