Cairn Energy has filed a case in a U.S. district court to enforce a $1.2 billion arbitration award it won in a tax dispute against India, a court document showed, ratcheting up pressure on the government to pay its dues. In December, an arbitration body awarded the British firm damages of more than $1.2 billion plus interest and costs.

The tribunal ruled India breached an investment treaty with Britain and said New Delhi was liable to pay. Cairn asked the U.S. court to recognise and confirm the award, including payments due since 2014 and interest compounded semi-annually, according to the Feb. 12 filing seen by Reuters.

The case marked a first step in Cairn’s efforts towards recovering its dues, potentially by seizing Indian assets, if the government did not pay, a source with knowledge of the arbitration case told Reuters. “If Cairn wins the case, it will be a step towards attaching and seizing Indian assets overseas, especially in the U.S.,”. Reuters reported last month that Cairn was identifying India’s overseas assets, including bank accounts and even Air India planes or Indian ships, that could be seized in the absence of a settlement.