West Midlands Deputy Police and Crime Commissioner Yvonne Mosquito complained about Police and Crime Commissioner David Jamieson four weeks before he decided to suspend her.
Ms Mosquito wrote a letter complaining about Mr Jamieson's behaviour towards her four weeks ago, the BBC has learnt.
Mr Jamieson later decided to suspend her after allegations she visited a murder victim's family without informing officers, breaching protocol.
Unite rejected the allegations.
Kenichi Phillips, 18, was killed as he sat in a car in St Mark's Crescent, in Birmingham, on 17 March.
The BBC has since learnt Ms Mosquito wrote a letter of complaint about the PCC's behaviour towards her, of which the PCC was aware, four weeks earlier.
Multiple issues were raised but there was no complaint about racial discrimination, a source told the BBC.
The later allegations against Ms Mosquito were reported by a "senior officer from the force" said Mr Jamieson, and if proven "could have potentially hindered and jeopardised a complex, sensitive and ongoing murder investigation".
Mr Jamieson confirmed he took the "very difficult decision to suspend the deputy PCC" with immediate effect, pending an internal investigation into potential gross misconduct.
There was "no connection between the decision [to suspend] and any other issues," his office said.
A spokesperson added Ms Mosquito had not made her complaint "formal" nor "initiated the resolution (or "grievance") procedure".
The Unite union, of which Ms Mosquito is a member, said: "We are appalled that information that should be private and confidential as part of the disciplinary process has been put into the public domain.
"We will also co-operate fully with any inquiry into Yvonne's alleged conduct."
Regarding the letter of complaint, Unite said it "would be giving Yvonne all necessary support, including legal advice, at this difficult time for her".
"However, It would not be appropriate to comment further at this stage."
Ms Mosquito did not reply to requests for comment.
- 25 March 2016
- 20 March 2016