Ukraine's parliament passed a law on Thursday (September 23) that will force its oligarchs to register and stay out of politics.
It comes a day after the attempted assassination of a top aide to President Volodymyr Zelenskiy.
Serhiy Shefir's car was sprayed with gunfire by unidentified individuals as he traveled between two villages outside the capital, Kyiv.
Zelenskiy's team have said the attack could have been a response to the reform.
The law formally defines an oligarch, and gives authorities the power to designate individuals who meet the criteria.
Oligarchs would be forbidden from financing political parties or taking part in privatizations.
Top officials, including the president and his staff, would also be required to declare any dealings they had with oligarchs.
Zelenskiy says the law is necessary to protect Ukraine from powerful businessmen, who have corrupted its political system and wielded influence over the media for decades.
His opponents are skeptical, and fear it will be applied selectively to concentrate more power in the president's hands.
Shefir was unharmed on Wednesday, though his driver was wounded.
Police are now searching for the weapon and interviewing possible witnesses, according to an interior ministry spokesperson.
Zelenskiy has vowed to tackle corruption and curb oligarch's influence since he won a landslide election in 2019.