The proper officer has to first issue a notice to the defaulting taxable person under section 32 of MGL requiring him to furnish the return within a specified period of time, which has to be a minimum of fifteen days as per section 46 of MGL. If the taxable person fails to file return within the given time, the proper officer shall proceed to assess the tax liability of the return defaulter to the best of his judgement taking into account all the relevant material available with him. This power is given under section 46 of MGL.