To improve the integrity of the market and protect the investors’ interests, this is an initiative taken by SEBI and the exchanges. There are two types of ASMs, one is short-term additional surveillance measures and other is long-term surveillance measures. 

To know more about these, you can refer to the NSE website. It covers the terms and conditions based on which stocks are moved to ASM as well as the surveillance actions relevant to these stocks. You can also find out which of the stocks are currently categorized under ASM. 

Stocks that are moved to ASM can’t be pledged. If in case a stock that you have pledged is moved under ASM then you can’t receive collateral margins for it. This is because according to ASM 100% of the margin has to be levied. The collateral value will decrease by the value of collateral obtained against that particular stock. You have the option of unpledging the stock or keep it pledged without collateral till it is removed from ASM.

Please note that corporate actions are not affected if a stock is under ASM. The shareholders are still eligible for all corporate benefits like bonus, dividend, stock split, etc. even when the stock is under ASM.