Hello Healdida,
Like (Cite Contribution) mentioned this could be a case of "Resource optimization".
Another possibility COULD be that the management could be feeling 'threatened' by your growing stature--especially since you mention it's a JV. Is the other Partner in the venture foreign? If yes, this is more likely, since many foreign JV partners look @ such a situation differently--which may not be in-tune with the Indian JV partner/management [meaning they feel threatened that YOU could replace them in the long-run--from the management perspective, NOT the investment perspective].
Given the situation, suggest LOOK @ IT DIFFERENTLY--the very fact that you seem to have increased the profits for the company & you are, sort of, the Bulwark for the company operations says a lot for your caliber & capabilities, like other members too pointed out.
Maybe it's HIS way of hinting to you that the time has come for you to move-on & encash your skills BETTER? You haven't mentioned which sector/domain you work in--but whichever sector you are in, your skills would be best suited for any company that's a Start-up OR a company that is looking for someone to handle the scaling-up of operations.
Like Ankita Shah mentioned, you can do a quick survey in your professional network the salary range for your exp level & see if this can enable you to handle the concerns in your present company--BUT at the same time, pl be mentally prepared to move-out IF that's what the management wants. Such a survey would help you in such an EVENTUALITY.
While understanding your wish to check all options, including the 'legal recourse' angle, pl note that you are DIFFERENT from others in one crucial aspect. You HEAD the show. And any legal action COULD have a bearing on your future--in the way companies 'perceive' your action. Not that 'legal action' is totally barred/to-be-avoided, but suggest treat it as AN option based on the cost-benefits. In this case, I see the long-term harm far higher than the short-term benefits. Hope you get the point.
To summarize, I can only repeat what Ankita Shah mentioned: "If they are not getting convinced, I do not think we can do much about it. Atleast ask them that for good time's sake they keep you till you get a next job or recommend you in their professional link".
All the Best.
Rgds,
TS