The tax officer has both powers to assess or reassess incomes. By the ruling in  16 ITR (Trib)-OL 35 (ITAT[Luck]) it is further desirable to have an assessment under either sections 143 or 144 before undertaking reassessment.
In this case the AO headed for reassessment soon after filing of return by the assessee without undertaking any assessment under sections 143/144, which route is held impermissible under the law.
On receipt of any notice under section 148/148A the first thing that the taxpayer should look for is the assessment order issued against the original return filed in the first instance. If that is unprocessed or if no order seen issued to him on the portal or otherwise than he may challenge the validity of notice itself.