Are there any laws regulating access to the International Space Station for an Indian company, for research such as microgravity tests?
Astronaut time, payload transfer capacity, instrument time and other resources on the ISS are divided among the partaking nations depending on their financial commitment to the project. Also, some of the partaking nations have modules which they can use exclusively.
However, all the partaking nations are allowed to sub-sell their time and resources.
When the ISRO or a private Indian company would like to place an experiment on the ISS, they could contract any of the ISS partners to perform the experiment for them using the resources allotted to the partner. The price is a matter of negotiation, but it will certainly not be cheap.