Russian Roman Abramovich, owner of Chelsea Football Club, became a Portuguese citizen in April 2021. On Thursday, Portugal's government said it opened an internal inquiry into the granting of Portuguese citizenship to the billionaire.

Roman Abramovich was granted Portuguese citizenship based on a law that offers naturalization to descendants of Sephardic Jews who were expelled from the Iberian Peninsula during the medieval Inquisition.

The survey by Portugal's Instituto dos Registos e Notariado (IRN), which provides nationality and passport services, comes amid criticism from some activists, commentators and politicians who say the law should be reviewed as they believe it is being used by oligarchs to gain a foothold in the EU.

"Everything indicates that behind a well-intentioned law a passport mafia was created," João Batalha, anti-corruption activist and founder of the Portuguese branch of Transparency International, wrote on Twitter.

The truth is that there is little known history of Sephardic Jews in Russia, although Abramovich is a common surname of Ashkenazi Jewish origin.

The Ministry of Justice said that the inquiry was a standard process.

"It is a normal procedure adopted whenever there are situations or news that refer to any possible irregularity in the procedure carried out," advances Reuters citing a statement from the Portuguese ministry.

"The IRN only intends to establish beyond any doubt whether...there has been any kind of irregularity," he added.

A spokeswoman for Abramovich said that he and his staff "welcome any review, as it will only demonstrate that citizenship was obtained according to the rules."

Thousands of Israeli Jews have obtained Portuguese citizenship since the law was passed in 2015. The number of such applications has increased in Portugal since a similar offer of citizenship to Sephardic Jews by Spain ended in 2019.