A motion put forward by an opposition MP aims to have parliament declare South Africa's entire Free State province, which borders Lesotho, as well as areas of four more regions to be part of the small mountain kingdom.
"I hope that after the debate, our country will be returned to us as should have long been," the lawmaker, Tsepo Lipholo of the Basotho Convenient Movement (BCM) told AFP ahead of the debate.
The disputed regions where historically inhabited by the Basothos, a people from southern Africa's Bantu ethnic group, who represent a large majority in Lesotho.
Lipholo is the sole BCM lawmaker in Lesotho's 120-seat National Assembly.
The return of Basothos' lands was the party's top campaign issue ahead of national elections last year and is a popular topic among the opposition.
The government looks unlikely to pick a fight with Pretoria but has yet to comment on the issue.
Were the motion to pass in the assembly it would kick off a process that could see the territorial claim turned into law.
The motion is based on a 1962 United Nations resolution that recognized the right to self-determination and independence for the people of Basutoland - as Lesotho was then called.
Lesotho, with a population of about two million, is entirely surrounded by South Africa, population 60 million, and on which its economy largely depends.
Lesotho Lawmakers Look at Land Takeover
MASERU, LESOTHO - Lawmakers in Lesotho were to discuss on Wednesday whether the country should seek to reclaim large swathes of land from powerful neighbor South Africa.