A corporate governance advocacy group whose members include institutional investors that collectively manage assets of more than $10 trillion urged Tokyo's stock exchange on Friday not to delist disgraced Olympus Corp <7733.T>.

Olympus, a once-proud maker of cameras and medical equipment, has admitted to hiding losses for decades through improper accounting, but it has yet to disclose the extent of this concealment and what write downs it will now need to take.

The Asian Corporate Governance Association said in the letter that it supported the imposition of strong sanctions against the individuals concerned in the affair.

We are extremely concerned, however, at the possibility of Olympus being delisted from the Tokyo Stock Exchange -- even if it meets the December 14 deadline for its quarterly report, said the letter, dated November 17.

We believe that shareholders have already suffered enough due to the actions of Olympus executives and that a delisting would unfairly punish them and other stakeholders further, it said, adding that a delisting would also complicate Olympus' efforts to get back to normal operations.

As Olympus remains a going concern with healthy businesses in several market sectors and probably would not be delisted were it registered on another developed market exchange, we believe that a delisting would also harm Japan's reputation among international investors, the letter said.

The TSE has placed Olympus on a watch list, a possible prelude to delisting.

If Olympus fails to meet a December 14 deadline for filing its financial statement for the six-months to September, it will be automatically delisted. The bourse may still delist the shares depending on the scope of its past financial misstatements or if it finds involvement by organized crime syndicates in the loss-covering scheme.

(Reporting by Linda Sieg; Editing by Edwina Gibbs)