Interest u/s 234(b) & (c)

Many Salaried Assessees are receiving Intimation under 143(1) with interest charged u/s 234(b) & (c) for the Assessment Year 2017-18. The Assessee didn't have income other than Salaries. The PSU, where they employed deduct TDS and pay to Revenue regularly. Under this situation how IT Authorities impose penalty under 234(b)&(c).