The Singapore Exchange (SGX) has asked several listed firms why they failed to disclose enough information in their annual reports about the remuneration paid to key executives.
High-profile companies Noble Group, Osim International, KS Energy and Sakae Holdings were among those questioned in the past two weeks.
Companies are not required to adhere to the code of corporate governance.
But listing rules require that firms which do not follow the guidelines must cite their reasons in the annual reports.
If they do not, the SGX sends out queries to such firms to remind them that they need to explain their reasons.
This has led to the questions over remuneration.
The code encourages firms to disclose details such as remuneration of their directors, the chief executive and at least the top five key management staff who are not also directors.
But some firms are reluctant to give away what they regard as commercially sensitive information, fearing it will encourage talent-poaching.
Noble Group's 2012 annual report listed the directors, the payout structure in percentages and remuneration bands of below $250,000 and above $1.5 million.
When asked by the SGX why it left the upper limit on salaries open, Noble said providing more details "would be disadvantageous to the interests of the company and its subsidiaries".
It cited reasons such as highly competitive industry conditions and sensitivity and confidentiality of remuneration matters.
By comparison, fellow commodity player Olam International provided an additional banding range for directors' salaries.
Payouts were separated into three categories: below $250,000, between $800,000 and $1.7 million and above $1.7 million.
Osim International also cited competitive reasons when queried by SGX. It told The Straits Times that it did not want rivals to know the pay of key executives.
Its spokesman said on Thursday: "We should not subject people to public exposure of their exact income as it could be more detrimental to the company. The purpose of corporate transparency is to protect the firm, not increase its risk. Providing a range is sufficient for investors to decide if they want to invest."
Mr Terence Wong, the co-head of research at DMG & Partners Securities, said the banding system is a reasonable guideline but he hopes firms will state an upper limit for the salary ranges.
Corporate governance expert Mak Yuen Teen, an associate professor at the National University of Singapore, said firms citing the fear of talent-poaching are just looking for an "excuse" to hold back information.
"Singapore has low transparency when it comes to executives' pay compared with other developed cities in Australia, Europe and the United States," he added.
"In Hong Kong, the listing rules require the salaries of every director to be explicitly spelt out. Is there no competition for talent in Hong Kong?"
Mr David Gerald, the president of the Securities Investors Association (Singapore), said: "Disclosure of top senior management salaries is important for shareholders considering to invest in a company.
"Research reveals that imbalances remuneration systems can hurt a company's long-term strategy by encouraging a focus on short-term gains.
"Well-performing managers must be paid well but not on a short-term basis."
Some firms do opt for full transparency. SingTel and fish breeder Qian Hu disclose the exact salary packages paid to top management and directors.
Qian Hu managing director Kenny Yap said: "Critics often say that family-run businesses are not transparent enough.
"By doing so, I'm accountable to both shareholders and employees, who can see how much the top executives earn."
He added that the competition-for-talent reason will be debunked if all listed companies are required to report actual remuneration figures as it will even out the playing field.
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