An open letter to the London Academy of Music and Dramatic Art (LAMDA) board says it "stands in solidarity" with its ex-Director Sarah Frankcom following her resignation in August.
More than 100 signatories shared their disappointment. They said their trust in the board has been damaged and that Franckom has not "been supported as she should have been".
The letter alleges a lack of accountability in the ongoing investigation into Frankcom's leadership.
It says interviews with internal staff have begun "without an adequate, transparent record of minutes" and alleges Chairman Shaun Woodward has called up staff off record.
At the time of publication, the letter had been co-signed by 24 of LAMDA’s permanent staff, 43 of its freelance practitioners, associate artists and visiting directors and 33 industry professionals.
LAMDA, which is conducting an inquiry into claims against Franckom, declined to comment.