Lam was appointed to the Blues head coaching role last week, but was allowed to stay as the Auckland provincial head coach until the end of August, or round six of the national competition.
When Highlanders coach Glenn Moore was appointed in August last year he was forced out of his role as Otago provincial assistant coach within a week, as the NZRU ruled he could not continue in his assistant role.
But NZRU professional services manager Neil Sorenson said there was no double standard and each situation was treated differently.
He said Moore was only the assistant coach and the competition was already under way, while Lam was the head coach of Auckland and the Air New Zealand Cup competition was starting in under a month.
Sorenson said Lam's being a head coach was the key difference, as he was heavily involved in the Auckland campaign.
He said there was no hard-and-fast rule set by the union, and each case would be treated on its merits.
He said the NZRU rule was a person could not coach a Super 14 franchise and a provincial team in the same year, and Lam did not fall into this category.
Sorenson said the Auckland Rugby Union was moving quickly to replace Lam and he hoped for a replacement to be named within the next five to six weeks.
Lam's assistant with Auckland, former All Black and Welsh fullback Shane Howarth, is tipped to take on the top job.
Otago Rugby Football Union chief executive Richard Reid said he was perfectly happy with the situation.
The wrong decision had probably been made last year, while the right decision was made this year, Reid said.
