Four ex-managers from the 794-bedroom Hilton Metropole in Birmingham have pleaded guilty to conspiracy to steal.
Joseph Hockridge, 35, from Middlesbrough, Justin Clark-Vine, 33, from Tamworth, Staffordshire, Rachel Clark, 27, from Solihull, West Midlands, and John Flynn, 41, from Castle Bromwich, West Midlands, entered guilty pleas at Warwick Crown Court on 19 May.
The former Hilton event managers fraudulently claimed agents' fees on conference bookings between January 2000 and December 2003. Two former banqueting managers pleaded not guilty to the same charge.
Roger Lyne, 53, and John Kreft, 43, both from Solihull, will reappear before the court on 30 June to fix a trial date. Legal arguments continue about whether a seventh defendant, John Palmer, 42, from Birmingham, should also be prosecuted.
The prosecution alleges that the total amount stolen by all defendants was more than 250,000. The seven defendants will be sentenced after the trial.
A Hilton spokesman said the company is unable to comment on any ongoing police investigation.