The 23-year-old with well-documented alcohol problems has admitted his involvement in the incident after a private house party which is now being investigated by his team and the New Zealand Rugby Union.
"We and the Crusaders were very disappointed to learn of this incident. As a result, the NZRU has initiated misconduct proceedings against Zac," NZRU chief executive Steve Tew said in a statement.
"We will be meeting with Zac and his representative in the following week to discuss the matter, and next steps.
"As his employer, we want to ensure that the process respects Zac's right to a fair hearing so we do not wish to comment further at this stage," Tew added.
The 10-Test All Black is hardly new to misconduct probes and was banned for four games and ordered to undergo alcohol counselling after a naked, drunken rampage in the Cook Islands in November 2011.
Guildford had previously apologised for his "excessive drinking" and narrowly escaped a playing ban at the 2011 World Cup after an alcohol-related incident prior to the tournament beginning.
- Sports & Recreation