While endorsing the views by Shri.Umakanthan, I would like to add that in private sector it is easy to organise provided there is no resistance by the employer or owner. Invariably you will find resistance to organise in private sector by the employer or owner.
Was your query related to any SPECIFIC situation OR a general research query?
IF related to any specific situation, pl elaborate.
The word 'Union' is more often associated with PSUs. In Private sector, the word used is more often than not 'Association'--Keshav Korgaonkar would be bale to give IF there are any legal reasons for this.
The most recent & well-known Private sector Union [in-effect] has been the Nokia one, which handled really very well the employees' interests during the Nokia Chennai plant closure.
Forming a trade union in private sector is generally difficult because of the natural apathy of most of the employers towards unionization. Particularly when the industry is knowledge-based and the employability of the employees is also more, as in the cases of I.T and I.T.E.S, unionization comes to nought. After the advent of globalisation, economies have become highly market-driven demanding liberal privatisation and more flexibility of employment. The political affliation of every central trade union stands in the way of flexible employment for obvious reasons other than workers' interests. That is why the apathy of private sector employers towards unionization is always on the increase and they try to scuttle every move in this direction. In respect of public sector, unionization is relatively easier since almost all the political parties have their own labour wings and their primacy is dependent upon which party is in power. No C.E.O of any public sector organization can act in the manner he likes in respect of trade union relations. Since Public Enterprise is mainly an effort of employment generation, the in-take of employment will be relatively larger and this would easily lead to unionization right from the inception level with the guidance of major central trade unions.
Regarding functional aspect, important issues like wage revision and other service conditions would be taken care of by the central leaders who are very adept in the art of negotiations and highly influential in making policy decisons. So, plant level union leaders are left with only day to day problems within the plant and keeping the membership intact.
In coercive activities like strike, work-stoppage etc no difference.
Larger the membership of the trade union irrespective of its sector, more effective will be its strength and bargaining power because of its more seasoned and matured outside leadership.