China’s banking regulator has ordered shareholders that have acquired more than five percent stakes in commercial banks through the use of financial products like insurance and asset management schemes to reduce their holdings within a year.

The regulation, dated Feb. 2 but made public late on Friday, is the latest in a series of measures to control risk and excessive leverage in the financial system, with everything from doggy lending practices to shadow banking under the microscope.

The regulator also said in a separate online statement that it “strictly forbids shareholders from imposing inappropriate control over banks and seeking illegitimate interests.”

The CBRC said it would investigate whether commercial banks’ shareholders were using their own, legally obtained funds for investment and whether they were holding stakes for other parties.

Any other existing stake purchase of more than five percent by investors and their related parties must seek approval by the CBRC within six months.

The new rules follow guidelines released in January that required major shareholders to disclose their ownership structures up to the ultimate beneficial holder.

The CBRC is drafting another set of new rules on shareholding custodianship to further increase transparency and standardize the management of banks’ shareholding structures, it added.