He was not sure exactly what date Edinburgh Realty had contacted its tenants, but believed it was about two weeks before they were expected to make a decision.
The letter, which was originally reported by student radio station Radio One, said the flats would be advertised from June 7 if a new lease was not arranged.
A follow-up email sent to tenants on April 28 amended the initial statement by saying Edinburgh Realty would begin getting properties ready for advertising, but listings would only be released to the public once confirmation had been received about whether residents wanted to continue their tenancy.
Le Sueur said he was pleased the company had fallen into line regarding its legal obligations and from his perspective the matter had been resolved.
OUSA student support manager Sage Burke said most landlords were good but a few had room to improve.
His message for students and landlords was the same: be professional and aware of your rights and responsibilities.
"Think about what you can do to work with the other party to ensure that it's a successful tenancy," he said.
Otago Property Investors Association president Kathryn Seque said the best outcome under the new law would be for students and landlords to work together.
Students should let landlords know when they knew their plans for next year, so landlords could rent the place to others.
It was as yet unclear how Dunedin's rental market would be affected by the new law, she said.
There was a potential risk that first-year students coming out of halls might struggle to find flats.
"We are trying to hold them back a bit, but the rumours go around the halls of residence like they always do this time of year," she said.
Edinburgh Realty managing director Peter Wilson said the company had been "inundated" since February with inquiries for next year's flats, as tenants were desperate to get published listings for available flats.
A publication comes out in June each year and is driven by the high demand from students.
The tenants from the advertised flats had already given notice they would vacate at the end of their current tenancy, Wilson said.