Notice of Demand [Section 156] :

When any tax, interest, penalty or fine or any other sum is payable consequent to any order passed under this Act, the Assessing Officer shall serve upon the assessee a notice of demand in the prescribed form, specifying the sum so payable.

The Apex Court in Sri Mohan Wahi v. CIT, 248 ITR 799 has held that failure to serve notice of demand renders the recovery proceedings invalid.

An intimation under section 143(1) or section 200A(1) or section 206CB(1) would be deemed to be a notice of demand for the purpose of section 156, where any sum is determined to be payable by the assessee under section 143(1) or by the deductor under section 200A(1) or by the collector under section 206CB(1).