Want to acquire lock on tables where primary of one table is foreignkey on othere

 I write this email to get the information about locking which I am not getting from anywhere.

Actually I have acquired a "Select for Update" on a table whose id is refrence as a foreign key on another table So I want those table won't update until there is lock. Is it possible? Becuase postgres is acquiring lock but AccessShare Lock which allow to write on those table How I restrict this.

Thanks and Regards 

Abhishek