The financial regulator is inspecting the nation’s top four commercial banks as they are plagued by allegations of corruption. It is unusual for the Financial Supervisory Service to inspect the four largest banks ― Kookmin, Hana, Shinhan and Woori ― at the same time.

For Kookmin Bank, the FSS has launched an intensive probe into the recent allegations that the bank’s branch in Tokyo had been involved in irregularities to create slush funds.

The Tokyo branch is suspected of having extended illegal loans amounting to 400 billion won, for which it allegedly received high commission fees. The branch is also suspected of having sent about 2 billion won in slush funds to the bank’s former top officials.

The branch’s alleged misconduct was reported to the FSS by the lender’s internal audit team. It was also brought to the regulator’s attention by the Financial Services Agency of Japan.

The FSS said FSA officials recently visited Seoul to share the findings of their investigations into allegations that the branch had laundered 450 million yen for the yakuza in 2011.

If the allegations turn out to be true, it will bring shame not only on the bank but on the nation. Kookmin is one of the banks that represent the nation’s banking industry. As such, the FSS should thoroughly investigate the scandal and mete out punishments to those responsible.

For Hana Bank, the FSS is zeroing in on allegations of irregularities related to Kim Seung-yu, former head of Hana Financial Group, the bank’s parent company. The bank owns about 4,000 artworks. Kim is known to be an art lover but the FSS suspects there is more to the bank’s unusually large art collection.

Shinhan Bank is under scrutiny as its officials illegally looked into the bank accounts of politicians and government officials, while Woori Bank is being investigated for incomplete sales of trust products to investors.

The top four banks are suspected of having committed many irregularities under the previous government as regulators could not oversee them properly because they were run by close friends of former President Lee Myung-bak.

In this regard, the ongoing inspections are necessary. But the FSS cannot avoid criticism for its failure to supervise the banks in a preemptive way. The recent Tong Yang group debacle showed the FSS failed to play its watchdog role properly.

So much so that in his confirmation hearing Tuesday, Board of Audit and Inspection Chairman nominee Hwang Chan-hyun said he would, if appointed, conduct an inspection of the financial regulator. He should do it.