Spain is threatening Argentina with unspecified retaliation if it nationalises Spanish oil company Repsol's operations in Argentina - known as YPF.
Buenos Aires has been pressuring YPF and accusing it - along with other major energy firms - of inadequate production and of not investing enough.
There are reports that Argentina has plans to take a controlling interest in YPF which is 57.4 percent owned by Repsol and Argentina's largest oil and gas company.
A chorus of top Spanish officials has warned against that.
Spain's secretary of state for EU affairs Inigo Mendez de Vigo warned that Argentina would become "an international pariah" if it were to go through with such plans.
"I think that if it happens, it would be very bad news for everybody, but also for Argentina because in the international community we live in, breaking the rules bears a cost," he said.
"If a (nationalisation) decision were taken it would be very negative for Spanish interests and the duty of this government is to defend Spain's interests with all its might," Deputy Prime Minister Soraya Saenz de Santamaria said after a weekly cabinet meeting.
"If the government had to take measures it would, without a doubt," she added.
The Industry Minister Jose Manuel Soria said: "If somewhere in the world there are acts of hostility against the interests of Spanish companies, the government will interpret them as hostility to the government of Spain and Spain itself."
Repsol's share slumped on Friday as YPF provides a quarter of its operating profits.
A proposal by YPF to boost investment to a record 2.6 billion euros was rejected as inadequate by the Argentinean government.