NEW DELHI (Reuters) - ArcelorMittal's India joint venture has sued New Delhi for rejecting imports of a steelmaking raw material, saying it was incorrectly imposing import curbs retroactively, escalating its fight over a policy change that is hurting its business, documents show.

India's government imposed curbs on imports of low-ash metallurgical coke, or met coke, starting in January, with country-specific quotas to help domestic suppliers. That has spooked big players like ArcelorMittal Nippon Steel India which are concerned about quality issues with local met coke.

ArcelorMittal Nippon has already warned New Delhi privately that it may have to severely curtail steelmaking and delay any expansions due to the curbs.

In an escalation of the tussle, the company challenged Indian authorities at the Delhi High Court on March 5 for rejecting 168,300 million tonnes of met coke import orders from Indonesia and Poland which were placed before the restrictions kicked in.

India's government rejected its import request, saying the company had sufficient quantities of met coke already, but that decision "militates against" the country's free trade policy which allows for the import of already placed orders before restrictions are imposed, ArcelorMittal Nippon said in its court filing, which Reuters is the first to report.

New Delhi was seeking to apply its policy change retroactively, and this "creates uncertainty and lack of confidence among traders and investors regarding the policy assurances," the 290-page filing said.

The company, a 60-40 joint venture between Luxembourg-based ArcelorMittal and Japan's Nippon Steel, did not respond to a request for comment.

India's government also did not respond. A March 6 court order shows officials have to respond to ArcelorMittal Nippon's plea by next week.

Bigger rival JSW Steel also has dragged the Indian government to the Delhi High Court over delays in clearing earlier met coke imports worth around $90 million, saying the proper implementation of policies is essential for "businesses to plan and operate effectively," court papers show.

A decision on that plea is pending. JSW declined to comment.

India's Steel Secretary Sandeep Poundrik told reporters on Wednesday enough domestic met coke was available and companies only want to resort to imports as they are $50-100 per tonne cheaper.

ArcelorMittal Nippon argued in its court filing that New Delhi's move would impact its production and expose "it to significant financial harm (both on account of breach of contractual obligations to its suppliers and customers)."

It added the move could cost the company $25 million per consignment. And it also faces vessel detention charges of $27,004 per day if permissions are delayed, court papers show.

In a confidential letter to the Indian government on February 19, the company had sounded an alarm bell due to import curbs, saying it could be forced to shut down its blast furnace operation from June or will reduce production from April.

ArcelorMittal Nippon has a 5% share of India's steelmaking market, which has an annual capacity of 200 million metric tons.

India's imports of low-ash met coke have more than doubled over the four years and New Delhi has restricted total overseas purchases to 1.4 million metric tons between January and June.