Travel allowance not being paid - threatened to be fired if we don't go

I am working in client side location for my company. The client side location is very far away from my location due to which I have claim travel allowance from my company. But my company is not willing to provide any allowance. They are saying you have to do it without allowance and if I say no to it , my manager told me, he will be fire me if I don't go.
Even in the HR policy it is return of travel allowance, still HR don't support. Its a small firm and it is doing injustice to their employees. How do I deal with this situation, because I don't want my future to me affected because of all this crap. Please tell me my employees right in this situation and do they have right to fire me. Can I seeking help of law.
Thanks in advance for all the valuable suggestion. please reply.

Ideally speaking company should provide conveyance expenditure for visiting client.
So request your HOD also to take up the matter of providing conveyance or reimbursement of expenditure involved in visiting clients.
Are all other employees facing similar problem?

Other employee dont stand for there rights and dont ask, because HR people dont support there employees. Basically worried about the job security. They say policy is revise, and they cannot provide travel allowances. If employee not doing client said working he is going against the company policy, that will cost him loss of job and in my case manager said will fire you. I neva had such experience working for this company. please advice on my employee rights on this and how to take legally.