Campaigners will lodge a formal complaint to the BBC for a serious breach of their impartiality and Charter guidelines.
 
The complaint from campaign group Republic follows Prince William's appearance on The Graham Norton Show.
 
The show appears to have been co-opted for the promotion of the Earthshot Prize, an independent charity with close ties to William.
 
The BBC's own guidelines say the corporation must not endorse or support individual charities except for its own official corporate charities, such as Children in Need.
 
In 2013, the BBC reprimanded Norton and his production company after Norton wore a World AIDS Day ribbon on his show. 
 
At the time, the BBC said its guidelines meant the corporation "...must remain independent and distanced from government initiatives, campaigners, charities and their agendas, no matter how apparently worthy the cause or how much their message appears to be accepted or uncontroversial."
 
Friday's Graham Norton Show featured William alongside other guests who all had links with Earthshot. A significant portion of the show was highlighting the charity in a wholly uncritical fashion.
 
Republic has also challenged the BBC over its uncritical promotion of William, who is a publicly funded figure who holds public office.
 
Speaking for Republic, Graham Smith said today:
 
"The BBC has an appalling track record when it comes to royal partiality. They fawn and celebrate and join in with the royal PR machine. They exercise poor judgement time and again, failing to represent either the monarchy or public attitudes fairly or accurately."
 
"This latest programme is a case in point. William wants to do this because the royals know the writing is on the wall. They can see the falling polls and they can see the rising voices of opposition."
 
"The BBC's job is to report and reflect on the failings of the monarchy and changing attitudes towards the institution. Instead, they allow themselves to be wholly co-opted by the palace PR machine."
 
"The latest coverage is nothing more than PR slop, designed to shore up flagging support for the royals. The BBC's collusion with the royals fails the British public, whether royalist, republican or indifferent."