The Indian Express report has more information.

see indianexpress.com/article/india/india-others/moef-to-solicitor-general-is-plea-in-sc-against-swatanter-kumar-a-valid-complaint/

I quote:

"The NGT Act empowers the Central government to remove the tribunal’s chairperson if it is found he has “abused his position so as to render his continuance in office prejudicial to public interest”.
Proceedings to remove any member of the tribunal, however, can only start after the government receives a “written complaint” relating to his alleged misbehaviour.
After the writ petition was filed against Kumar, the Supreme Court issued notice to the Centre – the government’s reply is expected on Thursday. The MoEF, which has received a copy of the writ petition, wants to know if this petition could potentially trigger an investigation under the NGT Act against Kumar.
If the SG responds to the MoEF’s query in the affirmative – that is, to consider the writ petition as a complaint – the government is bound by the NGT Rules to do a “preliminary scrutiny” of the same.
After a preliminary enquiry, the government may set up a committee – comprising the cabinet secretary and secretaries of the ministries of environment and forests, and law and justice – to investigate the complaint.
This committee would place its findings before a Supreme Court judge, who would conclude the investigation and offer his recommendations to the government. During this final stage, the Centre may suspend the tribunal member from office, according to the statute.
The Indian Express has learnt the ministry, internally, is of the opinion the NGT Act would not bear on Kumar’s alleged conduct because it pertains to his tenure in the Supreme Court but still wants the SG’s opinion.
Kumar took over as NGT head in December 2012, more than a year after the alleged incident is said to have taken place."

I don't think the NGT Act would apply to the investigation of a sexual harassment complaint. First, the sexual harassment allegations pertain to Swatanter Kumar's time as a Supreme Court judge.

The Vishakha guidelines squarely apply here and not the NGT Act. Of course, consequences under the NGT Act might follow if a Vishakha committee rules against Swatanter Kumar.

I hope the intent behind this is not to refer the sexual harassment complaint for a preliminary inquiry by the government which could be used to hush up the matter.