I have recently finished a paper and send it to my supervisor for review. He corrected it and before submission, he added some authors (some labmates, collaborators) who have no idea about my project. Also, he did not even ask me before adding though I worked so hard for that project. How ethical it is? Because he is my supervisor, I could not raise my voice. But I think this is not right. Is it so common phenomenon in academia?
No, it is not ethical. Yes, it is common.
Particularly for countries that have requirements on absolute number of papers to be published by grad students prior to graduation, this is a relatively common practice. Many journals now ask for the authors to explicitly list what was each author's contribution to the article, but of course this is also quite easily padded.
A question to consider, however, is whether or not these other authors had any contribution to your project you're not aware of. For example, if you are doing experimental work, perhaps they built the system you use to acquire your data - even if they have no idea about your data or experiments. In these cases some argument could be made for their inclusion. Whether that's true or not in your case is up to you.
As to what to do about it, if you have a good relationship with your advisor, ask him why they are being added using the most neutral language you can find. They may have some very good reason for adding them. If you don't agree, you can voice your disagreement and go from there. If you have a poor relationship with your advisor, you probably will just have to accept it and move on. I don't recommend secretly or "accidentally" going against your advisor's wishes since this will likely backfire, and they will in any case simply correct it at the proof stage.
This is known as padding and is not ethical.
Will you take a stand?
Well, will that affect your supervisor / student relationship? Your degree completion?
That is probably why this practice happens and will continue to happen. You have to decide if you will talk to your supervisor, if that fails then the department head, then the head of research or even contact the editor.
The consequences could be huge for you...
If it has not been submitted yet and you do the submission, then you could make a "mistake" and remove those names... "Sorry I sent the wrong version"...