Hello Anamika,
Perhaps my views differ a little to the earlier suggestions. In my opinion, if your Company is registered under Factories Act / Companies Act, then, there must be its own Certified Standing Orders or it must be following Model Standing Orders, as the case may be. These Standing Orders contain the Dos & Don'ts for each and every employee employed in the Company on which they apply. In some Companies there is separate set of rules for executives which they call Conduct, Discipline & Appeal (CDA) Rules.
Once an individual has accepted the offer of appointment, it is deemed that he has accepted and agreed to the terms and conditions of employment too, whether or not he has separately signed a document of acceptance. There is one line given in the appointment letters that "accepting the offer of appointment shall mean that you accept the terms and conditions of employment and shall abide by them". Even if this line is not there, joining after offer of appointment means the same, but I strongly recommend to make a mention of this statement in future offers, if not being done at present.
AK Jain