In India, the name "Trade Union" is not viewed comfortably by the majority of employers. Hence, if you are really interested, kindly change to a softer name like "xx(Company's Name) Labour Union" and do not go for immediate affiliation with any major Trade Union. Request your top management for recognition by explaining to them the purpose of your union.
Presently, labor unions are legally recognized as representatives of workers in many industries in India. Unless your company is a medieval one, they will generally welcome you and will even make you participate in decision-making processes to develop a participative culture among workers. A satisfied worker is always an asset for the organization.
Your memorandum should specifically state your vision and mission. It should clearly state that the aim is to bring workers' legal welfare measures and their rights to the management and negotiate with the management for enlightening the same.
I, as an HR consultant, have achieved good results.