He said the rosters affected about 35 doctors across medicine, surgery, paediatrics and obstetrics.
"The DHB has decreased the number of nights worked consecutively from seven to four on two of their three affected rosters, but these doctors still work 12 day shifts in a row without a break.
"Of even more concern is that our medical registrars looking after some of our sickest patients suffering strokes, heart attacks, pneumonia and other such conditions, have had no improvements made to their roster at all."
Dr Reynolds said on some rosters doctors worked 12 shifts in a row including two 16-hour days.
While he wouldn't comment specifically he said doctors were certainly feeling tired by days 11 and 12.
By the last two days of the shift they found they were "starting to drop the balls".
Speaking out wasn't something they wanted to do, he said.
"This is by no means something that we have taken lightly."
Lakes District Health Board said as it was currently in negotiation regarding this group of staff, it would not comment at this time.