add one more new column supplytypecheck, check if supply type IMPG that should be Y else N

Question

df["supplyType"]

0     TAX
1     TAX
2     TAX
3     TAX
4     TAX
5     TAX
6    IMPG
Name: SupplyType, dtype: object

Question is when supplyType is IMPG i should add a new column supplytypecheck with value "Y" for True else "Y" for false

i done it like

a =df["SupplyType"].index

for i in a:
    
    if (df["SupplyType"][i]) == "IMPG":
        df["supplytypecheck"] = "Y"
    else:
        df["supplytypecheck"] = "N"

It givens all df["supplytypecheck"] values as "Y" but "Y" should only be value for last index because it equals to IMPG all the upper values are equal to TAX.

Please help how to solve it