section 25

Company: Under Section 25 of the company's act, an association formed or to be formed:

a) For the purposes of promoting commerce, art, science, religion, charity ot any other useful object
b) With intention to apply its profits or other income for promoting its objects, and
c) Which prohibits payment of any dividend to its members,
Is permitted to be incorporated without addition of the word "Limited" or "Private Limited". Procedure for applying is same as applicable in the case of all companies.

If the registrar is satisfied that all formalities have been complied with, he will issue a certificate of incorporation from which date the company comes into existence.

Note: An association already registered as a company, may also apply for a licence u/s 25.
 

partnership firms are allowed 2 become member of sec 25 companies...! (exceptional case)

so in my opinion AOP's are also allowed