In a long-running dispute with Estyn, EGIS also raised concerns that inspection findings overall are giving a misleading impression of school standards in Wales. And it complained about Estyn's response to these concerns.
But an independent review, published last week, concluded that Estyn had responded appropriately to EGIS's complaints. Adjudicator Elizabeth Derrington said the issue had got "seriously out of hand", with the two parties exchanging 50 letters in a year - eight of them in one day.
Estyn claimed it had been vindicated by her report, but EGIS said it was a whitewash and has lodged a complaint with the local government ombudsman.
EGIS, run by former Gwent education director David Griffiths and his wife, originally complained to Estyn that its employees had been "abused and harassed" by five schools.
It claimed a culture has developed of schools complaining when they are unhappy with findings. With inspectors under pressure to produce positive reports, inspection findings for Wales are also overly positive. EGIS said only 13 schools had been put in special measures in Wales compared to around 1,800 in England.
But Ms Derrington said Estyn had responded appropriately. Following an incident where EGIS employees had faced "aggressive feedback", Estyn agreed that inspectors should withdraw from meetings if they felt threatened by school staff. No other contractors had complained of bullying.
The agency also highlighted its work with English inspection agency Ofsted.
Estyn claimed that socio-economic differences meant there were fewer failing schools in Wales than England.