MADRID Spain has collected 2.9 billion euros ($3.07 billion) this year with the windfall taxes imposed on power companies and banks, acting Budget Minister Maria Jesus Montero said on Wednesday.

"We have always said that it is reasonable for those who have more to contribute more. It means contributing to the common good," Montero said in an interview with radio station Cadena Ser.

Banks and energy companies have paid 1.4 billion euros -- 827 million euros for energy companies and 626 million euros for banks -- in a second tax instalment in September, a similar amount to the first payment in February for a total sum of 2.9 billion euros, the Budget Ministry said.

Montero's comments come after Spain's Socialist Party and the hard-left group Sumar on Tuesday sealed a policy pact, which included the extension of then-windfall taxes on banks and energy companies, as they try to form a coalition government three months after an inconclusive election.

No details were released on how the new tax would be implemented. The potential coalition still needs to win the backing of other parties in the lower house.

While the tax on banks carries a charge of 4.8% on their net interest income and net commissions, the levy on energy companies includes a 1.2% tax on power utilities' sales.

Companies and banks appealed the tax before Spain's High Court.

"I hope that justice will prove us right. We legislate on the basis of legal certainty," Montero said.

($1 = 0.9448 euros)

(Reporting by Emma Pinedo, additional reporting by Jesús Aguado, editing by Inti Landauro and Bernadette Baum)