The NUT has branded as "wholly unacceptable" plans that could see more teachers punished for misdemeanors committed outside school.
The proposed code of conduct, which was drawn up by the General Teaching Council for England and covers behaviour both in and outside the classroom, has been heavily criticised by the union.
An NUT report, written as part of the consultation process, warns the code will cause "widespread confusion and uncertainty" as well as adding an unnecessary level of regulation governing teachers' performance inside school.
A TES investigation last year found that the number of outside-school offences being examined annually by the GTC had soared from 7 to 55 in the past four years. Of 632 hearings over that period, nearly a fifth concerned misconduct outside work.
The majority were driving incidents - largely drink-driving - with dishonesty, such as fraud, benefit fraud or theft a close second.
Mick Brookes, general secretary of the National Association of Head Teachers, has also criticised the scope of the new code.
Christine Blower, acting general secretary of the NUT, told The TES: "The GTC doesn't appear to have realised that in turning a set of aspirations into a disciplinary code, it has gone far too far. The danger, if the code is adopted without full-scale revision, is that it could lead to a wholly unacceptable interference into teachers' private lives."
The report says: "The NUT supports the GTC's aim of developing high-quality teacher professionalism and practice. It does not believe that this code, however, is the means of achieving this. By attempting to produce a comprehensive list of expected 'behaviours' that are applicable to all teachers in all contexts, the code raises more questions than it answers."
The code contains eight "core" values, which include working as part of a whole-school team and demonstrating "high standards of honesty and integrity" in order to "uphold public trust and confidence in the teaching profession".
Staff are also asked to "uphold the law and maintain standards of behaviour both inside and outside school that are appropriate given their membership of an important and responsible profession".
The NUT said this clause meant all teacher contracts would need to be revised and it would lead to a culture of being permanently on duty. It could also lead to confusion - for example, it seems to ban industrial action and curtails teachers' civil rights of protest.
The report says: "The value and point of a code should be to inform its readers that they are at risk when they break it, not to inform the readers about highly principled aspirations to which they should aim."
The union has called for the GTC to produce instead a simple list of things teachers should not do in their professional, rather than private, lives. They want this list to be "timeless" to make sure it becomes familiar.