After resigning and issuing a relieving and no dues letter, can a (former) employer trouble?

My former employer was targeting and humiliating all employees around 50 years of age, so that they will quit. Obviously, I resigned, got all the formal relieving letter, no dues certificate and all the settlement from the company. I got to know that my former employer was involved in some tax evasion and other activities - which i reported to relevant lae enforcing authorities - who raided my former employer and further action being taken.
In this scenario, what damager can my former employer do to me? Can he call my current employer and damage me or refuse employment verification in the future?
Please advise me.

Really it is a tricky situation. Your act of informing the Enforcement Authorities about your former employer's tax evasion may not be illegal as it was. But your motive behind the act and its timing shows your vengeance. I don't think that you would have disclosed your identity to the authorities and even if so they would not reveal the identity of informants in such cases.
Given the difficult temperament of your former employer, he may do any thing out of his rage only if it is known that you are the informant. Therefore, be cautious.

Thanks for the valuable feedback. Can my former employer refuse background verification ?

Dear member,
Your separation from the company and the IT raid on the previous employer were two unconnected things. In case if you had informed the IT authorities about the tax evasion then what you did was in the interest of the nation. But then while working for the interest of the nation it was important for you to keep in mind the interests of your career as well. What was the need to disclose that you had informed officially about the tax evasion to the IT authorities? You could have kept it secret also.
Income tax officials keep many high and mighty under surveillance. Obviously, they remain in touch with the near and dear ones of the tax evader. However, they do not blow up the name of their source. They maintain the utmost confidentiality.
Thanks,
Dinesh Divekar