A notice is served by the assessing officer u/s 142 (1) in two cases. Firstly, if the officer requires additional information and documents pertaining to your income tax returns. Secondly, if the return has not been filed but the officer wants the return to be filed. If you do not respond to the notice served under Section 142(1), you would face a penalty of INR 10,000, prosecution for up to 1 year or both.