Activist Boniface Mwangi's lawyer wants the Kenya Revenue Authority to release Deputy President William Ruto's tax returns.
On Monday, Mr Mwangi’s lead counsel, Gitobu Imanyara, also petitioned Independent Electoral and Boundaries Commission Chief Executive Officer Ezra Chiloba to provide wealth declaration returns for the period Mr Ruto has been the Deputy President.
Mr Imanyara’s letter reads in part: "The purpose of this letter is to request for information on wealth declaration returns of the plaintiff for the period he has been the Deputy President of the republic of Kenya.
"Our request is founded on Article 35 (1) (a) and (b) of the constitution and other relevant laws."
Mr Ruto had filed a defamation suit against Mr Mwangi on October 7, saying that a message posted by the activist on his Twitter page last month was false and malicious.
The activist had linked the country's second-in-command to the murder of businessman Jacob Juma.
Through lawyer Kioko Kilukumi, the Deputy President asked Mr Mwangi to delete the post and apologise within seven days or he would sue him.
But Mr Mwangi's lawyer filed a counter-claim on Friday, bringing the DP's integrity to question.
The letter further states: “We require you to provide us with the information as soon as possible but not later than Thursday (November 1, 2016) to enable our client to fully exercise his constitutional right to a fair hearing in the above case.”