NEW YORK (WABC) -- Mayor Bill de Blasio will be questioned voluntarily by federal prosecutors Friday in connection to fundraising activities for his campaign.An official familiar with the matter said that it is a voluntary interview. The mayor has had extensive preparation this week ahead of the meeting.Mayor de Blasio has not been subpoenaed. It is something of a tightrope walk for the mayor who has volunteered to answer questions, but has not been granted immunity from prosecution.Here is what he told reporters, early in the investigation:"I hold myself and my administration to the highest standards of integrity. I have been in public life for some time, I am a reformer for a reason," de Blasio said back on April 11, 2016.But investigators have been poring through finance records from the mayor's 2013 campaign, amid questions about how campaign officials solicited donations from the city's real estate and business sectors.The U.S. attorney and his staff are determined to find out whether individuals may have benefited from those donations.The mayor has insisted donors are not entitled to favoritism."If someone makes a donation, that's their choice, they should expect nothing in return," de Blasio said.Mayor de Blasio will be accompanied by counsel at the interview.