Spain's foreign minister has been fined 30,000 euros ($33,980) by the national stock market regulator for what it described as a very serious breach in rules intended to govern insider trading, an infringement that has on Tuesday triggered calls for his resignation.

The fine imposed by the National Securities Market Commission (CNMV) on Josep Borrell was for the sale of shares in energy company Abengoa while he was a board member and was published in Spain's official state bulletin.

"We impose on Mr. José Borrell Fontelles, for the commission of a very serious violation of article 282.6 of the Securities Market Law in the sale, on behalf of a third party, of 10,000 shares of Abengoa, SA, for 9,030 euros, on Nov. 24, 2015, having privileged information on this company," the bulletin said.

Borrell had acknowledged in Oct., when the commission said it would take action against him, that the sale "gave an impression of being irregular," but defended it by saying it only represented eight percent of his portfolio.

However, the penalty has led lawmaker Pablo Iglesias, leader of the left-wing Podemos party, to call for Borrell's resignation as the country's top diplomat.

"This government can not afford to have a minister sanctioned by the CNMV for selling shares with privileged information," Iglesias said. "I respect Borrell for his intelligence and his political stature and I think he will resign without us needing to demand it. Today he has an opportunity to set an example," he added.

Abengoa, a company that has invested heavily in renewable energy projects such as vast thermo-electric plants, managed to avoid bankruptcy in late Nov. 2015 by brokering an agreement with its creditors.

Borrell gave evidence in court on Oct. 2017 in a trial over large remunerations paid to Abengoa's former president, Felipe Benjumea and ex-CEO, Manuel Sánchez Ortega.

His declaration was only as a witness as he alleged that he was not present at the board meeting that approved the payments.