The publishing of the London mayor's official diary has revealed undisclosed conversations with News International (NI) executives.
Boris Johnson had phone calls with NI executives including Rebekah Brooks and James Murdoch during the height of the phone-hacking scandal.
Details were revealed after a request from the BBC and the intervention of the Information Commissioner.
A mayoral spokesman said Mr Johnson did not discuss the phone hacking scandal.
The release of the mayor's full official diary shows certain appointments in 2011 were not disclosed in a list of key engagements presented to the London Assembly at the monthly Mayor's Question Time.
On 28 April 2011, the mayor had a phone conversation with Rebekah Brooks, who was editor of the News of the World at the time much of the phone hacking is alleged to have taken place.
The diary, which lists more than 7,000 entries, also records a previously undisclosed telephone conversation with NI executive chairman James Murdoch on 6 May 2011.
Furthermore, the mayor met NI lobbyist Frederick Michel at City Hall on 11 May 2011 and had dinner with Prime Minister David Cameron on 17 May 2011, the diary revealed.
Lib Dem London Assembly leader Caroline Pidgeon said: "To discover that his published monthly engagements don't reflect his diary is quite extraordinary and leads to questions of why he's trying to hide some of his key engagements."
Labour London Assembly member Len Duvall said: "At the time the mayor had this pattern of contact is the time when police are investigating News International and individuals working for News International."
City Hall said some key engagements were not previously released "for commercial sensitive" reasons.
A Greater London Assembly spokesperson said: "At no point during these meetings or conversations did the mayor discuss Operation Weeting [Police investigation into phone hacking]."