Can my employer deduct half my salary for alleged poor performance without notice?

I work in a tech company in Bangalore and recently my employer deducted 50% of my salary citing poor performance. I've been with the company for over 2 years and this is the first time I'm hearing about any performance issues. They didn't give me any prior notice or documentation. I feel blindsided and financially strained. Is this deduction legal, and what steps can I take to challenge this?