Tymoshenko is serving a seven-year prison sentence on charges she abused her power when, as prime minister in 2009, she helped broker a natural gas deal with Russian energy company Gazprom.
Her lawyer, Serhiy Vlasenko, said Ukrainian authorities had posted fake emails between her daughter Eugenia and Hryhoriy Nemyria, the deputy director of her All-Ukrainian Union "Fatherland" party, the former leader's website reports.
Vlasenko stated that the publication of private correspondence was typically considered a criminal offense.
"As far as I know, the people whose addresses, real and fake, were revealed have already gone to the police in their countries to investigate," he was quoted as saying.
Radio Free Europe/Radio Liberty reports the emails are related to payments made to Western companies lobbying on behalf of Tymoshenko's interests.
Tymoshenko announced early this month she was waging a campaign of civil disobedience to protest her detention, which her supporters say is politically motivated. Last year, the leader of the country's Orange Revolution launched a brief hunger strike to protest prison conditions.
Her party took second in October parliamentary elections. European observers said those elections were a step backward for the country.