SANTIAGO, Sept 5 (Reuters) - Julio Ponce, ex-dictator Augusto Pinochet's former son-in-law who is at the center of a market trading scandal in Chile involving companies linked to his SQM fertilizer group, should resign, said an executive from one of the companies.
Rodrigo Zegers, an executive at Norte Grande who represents minority pension fund shareholders, said in a letter to Ponce that he should resign as chairman of SQM immediately.
Usually considered one of Latin America's least corrupt economies, Chile has been roiled in recent months by the affair involving the so-called "cascada" companies linked to SQM, which owns vast nitrate and lithium resources in the Atacama desert.
On Tuesday Ponce, the chairman of SQM , was fined nearly $70 million by the market regulator, the biggest individual fine out of a total $164 million levied in the market manipulation scandal.
Ponce should resign immediately due to "the severity of the sanctions imposed by the regulator, the seriousness of the alleged infractions and the economic and image damage caused to the cascadas, including Norte Grande," said Zegers in his letter.
Ponce and others are accused by the regulator of buying shares below market prices and selling them above market prices through the complex web of cascadas .
Business leaders and the government have also criticized the case for threatening investor confidence in Chile, although they have stopped short of demanding Ponce's resignation.
Billionaire Ponce, who controls SQM via stakes in the cascadas, acquired the company in the 1980s when he was the son-in-law of then-dictator Pinochet.
A lawyer for Ponce has said he will appeal the ruling.
Reporting by Rosalba O'Brien and Antonio de la Jara; Editing by Meredith Mazzilli