Does condo association need two signatures on their checks?

How would you handle violation of two signatory rule on checks and contracts? Our by-laws state that all contracts and checks must be executed by two of the board members (directors or officers). For decades checks were signed by two signatories. A few years ago the treasurer unilaterally decided it was ok to tell the bank that only one signature was needed, probably out of convenience. This is a concern because now the treasurer can write a check without any oversight. How would you proceed to correct this?