Hitting out at Gandhi, Kumar alleged she remained in her seat while her party's members created a ruckus in the Well of the House and did not try to stop them.
"It is painful that she did nothing... It was a black day in the history of Indian democracy," he told reporters after Speaker Sumitra Mahajan suspended six Congress members for causing "grave disorder" in the House with their "highly unbecoming" conduct.
Kumar claimed that the BJP never disrespected and defied the Chair like this during its 10 years in the opposition when the UPA ruled.
He said there was no reason for the Congress to protest as the Speaker was willing to allow a discussion on the matter and the government had agreed.
The Congress members were protesting over the lynching row.