"If the treaty is approved by parliament and receives the force of an international treaty, there will be no way of repealing it," Krisjanis Karins of New Times said, adding that could provoke a government crisis.
The treaty will enter into force upon ratification by both houses of parliament, which is to be completed in mid-May.
Latvia's government approved and submitted to parliament a law to ratify a border treaty with Russia April 10.
Russian and Latvian Prime Ministers Mikhail Fradkov and Aigars Kalvitis signed the border treaty in Moscow March 27, ending a drawn-out period of contention between the two post-Soviet neighbors.
The law was endorsed by all Cabinet members except those representing ultra-right parties, who deem it to be in breach of the country's Constitution.
By signing the treaty, EU member Latvia officially recognized the post-Soviet borders with Russia, backtracking on its earlier territorial claims on a district in the neighboring Russian region of Pskov, which was part of the Baltic state before World War II.
Talks on the accord, initialed in 1997, stalled last April with Riga adopting a unilateral declaration claiming the Russian territory and demanding that Russia acknowledge the Soviet Union's wartime aggression.
Moscow dismissed both claims as unfounded, and refused to sign the treaty unless Latvia dropped the declaration, which Latvia eventually agreed to do.
After the treaty was signed, a group of Latvian parliament members filed a lawsuit with the country's Constitutional Court claiming the treaty violated Latvia's Constitution.
The twenty-one MPs said the country's government had no right to sign the treaty without a referendum, because under the Constitution the people must approve all territorial changes.
The deputies said the government should have asked Latvians if they supported the decision to give up the country's claims to the Pytalovsky District in the Pskov Region in exchange for an improvement in political and economic ties with Moscow.
The Constitutional Court is to decide whether to consider the case or not within a month of the suit's filing.
