This is becoming a rules compendium, I really should build a rules wiki.
Here’s a rule from Conference 2016
Chapter 13 Clause II 2. A Aims and Values
NEW CLAUSE v. Members of the Labour group in administration must comply with the provisions of the Local Government Finance Act 1988 and subsequent revisions and shall not vote against or abstain on a vote in full Council to set a legal budget proposed by the administration. Members of the Labour Group shall not support any proposal to set an illegal budget. Any councillor who votes against or abstains on a Labour group policy decision in this matter may face disciplinary action.
What’s the penalty? This is worse in a Mayor led cabinet, because of the Mayor’s relationship with the budget, which can only be overturned by a ⅔ majority. Much then depends on the Group’s rules and transparency.