Shares in Vodafone slipped on Monday after its Chief Financial Officer suggested the firm could have to set large amounts of money aside to pay Indian tax bills.
The firm is in a battle with the Indian government over the payment of taxes stemming from its 2007 purchase of Hutchison Whampoa.
India's top court recently ruled that Vodafone would not have to pay the $2.2bn bill.
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However, the Indian government has since amended the law to retrospectively cover the taxation of cross-border transactions back as far as April 1, 1962.
"The situation has changed and we are looking at it," said CFO Andy Halford in an interview reported by Bloomberg.
The company's test over whether to make provision for the potentially massive bill "is now being applied differently against a recently introduced, albeit retrospective, legislation", he said.
Vodafone has vowed to pursue international arbitration if it is found liable for the bill, which the Indian government is chasing after the $10.7bn deal was done offshore through a Cayman Islands company controlled by Hong Kong-based Hutchison.
"We would be foolhardy to go backing off," Halford said
"Because it is mid flow and it is big we obviously need to avail ourselves of all the options that are in front of us."
Vodafone shares were down just under 1% after an hour's trading on Monday morning at 174.4p.
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