The two complaints against Butzbach relate to incidents several years ago when he was Fire Chief in Martinborough and on the board of UFBA.
One complaint relates to sexual harassment in what the complainant describes as a "hazing incident" in a restaurant in Martinborough.
The other complainant wants the terms of reference for the inquiry to "include sexual assault, sexual harassment, unwanted sexual advances, bullying, harassment and victimisation".
The terms of reference are yet to be determined.
The investigation comes as Fire and Emergency faces mounting pressure over the way it handles complaints over sexual assault, harassment and bullying.
Last week the Professional Fire Fighters Union expressed no confidence in FENZ leadership over its handling of complaints and said it was representing at least 10 volunteers who have lost faith in the UFBA to advocate for them.
RNZ has approached Butzbach for comment.
UFBA chairman Richie Smith told RNZ he could not comment on individual cases but that Butzbach remains in his role.
He said normally the UFBA does not run its own investigation process as "at the more serious end of the scale, they are dealt with by police or a FENZ process".
Smith said in the last year the UFBA was contacted for assistance and support in 109 new cases, 20 of which related to "bullying, harassment and exclusion".
Eighty-four of the 109 cases were resolved.
He said: "There have been some behavioural issues both with the paid firefighters that the [PFU] union represents, the 1800 of them, and through our ranks as well, and that is not acceptable.
"Anyone with concerns should be very free and come forward into a process that is robust, independent and timely."
