Social Democrat MP Inara Luigas said she is disappointed with the new border treaty and will vote against the ratification, despite all the parliament's factions saying they approve of the treaty.
Speaking on ETV on Tuesday, the day of the signing of the agreement, Luigas said an official border is very painful for many Setos, as many are left on the Russian side.
She said the Seto communities in the two countries have close ties, and in that sense, nothing will change.
The Seto people, numbering around 15,000, live in border areas in southeast Estonia and across the border in Russia. Luigas is a Seto activist, having led the Mikitamäe municipality in the Setomaa region, and published a cookbook of Seto food.
The last border agreement, the Treaty of Tartu in 1920, ceded Setomaa to Estonia, but it was split up during the Soviet occupation. After Estonia regained its independence in 1991, the region remained divided between the countries.