While poaching (as mentioned in the first answer) is a major problem, the loss of habitat tends to be just as much, if not more, of a problem. Even so, it is unlikely that we in the West can really do anything about it.
The only way to prevent loss of habitat is to prevent deforestation. Since we do not live in Russia or China, we cannot do anything directly (by pressuring our legislatures) to stop deforestation. Russia and China are two countries that are not well known for giving in to outside pressure, either. So, in my mind, the forest habitat of the tigers needs to be protected but I am not confident that Westerners can do anything to protect it.