If at any time it appears that the benefit of the federal act guarantying deposits in financial institutions has been withdrawn or is about to be withdrawn from the financial institution in which any public funds are deposited, the board having control of or supervision over such public funds immediately shall withdraw the full amount thereof from said financial institution, or forthwith shall require the usual bond required to secure the deposits of such public funds, and it is unlawful to continue any financial institution as a depository of public funds unless and until said bonds have been furnished.