The NYT code of ethics is the following:

Those working for us as journalists may not pose as anyone they are not -- for example, police officers or lawyers.

However, restaurant or travel reporters may break the code if they are wishing to "avoid special treatment."

Kristof's method featured him posting "provocative" comments and blog entries on Chinese sites in order to test out how long it was before the government deleted them, writes Bercovici. The columnist even had a Chinese woman who checked that his language sounded bona fide and "didn't have a strong American accent," reports the Arizona Daily Star.

Although pretending to be a Chinese national may be worse than pretending to be an officer to enter a crime scene, Bercovici wonders whether China's Communist Party may use the incident to "interfere with the reporting of other Times journalists operating in China" or claim "propaganda victory" by declaring that all the anti-Party criticism comes from "foreign propagandists like Kristof."

Kristof responded that he didn't "actively" deny his identity and that the NYT's guidelines say that its journalists "need not always announce their occupation when seeking information normally available to the public," writes Bercovici.  

Furthermore, he points out that he was being transparent by stating his methods in the column.

"The disclosure kind of helps when one is near ethical boundaries. It doesn't obviate issues but I think full disclosure helps," said Kristof.

Source: Portfolio.com, Arizona Daily Star