Spanish oil firm Repsol said it would sue any company that invests in its subsidiary YPF which has been nationalised by the Argentine government.
"We reserve the right to take legal action against any investor in YPF or its assets that have been illegally expropriated from Repsol," company spokesman Kristian Rix said.
Argentine President Cristina Kirchner announced on April 16 she was presenting legislation to parliament that would nationalise YPF, infuriating Madrid.
Argentina is looking for other investors in YPF and has urged Brazil's state-owned oil giant Petrobras to increase investment in the company.
Argentine ministers also plan to meet with US oil giants Chevron, Exxon and Conoco Phillips and Canadian company Talisman among others, the Argentine news agency Telam reported, citing officials.
Repsol executive chairman Antonio Brufau told a news conference last week that before the expropriation several international investors had shown an interest in the Spanish company's stake in YPF.
The Financial Times reported last week that Repsol had tried to sell its 57.4% stake to a Chinese firm shortly before the subsidiary was expropriated. It cited a source naming the company as China Petroleum & Chemical Corp (Sinopec).
The Argentine parliament is due to debate the expropriation plan on Wednesday. Repsol has vowed to sue over the seizure, saying it will seek $10.5 billion.
The Spanish government has denounced the expropriation as "hostile" and on Friday announced restrictions on imports of biodiesel from Argentina in retaliation.