In case of an amalgamation, supplies effected for the period from effective date till the date of order of the Court between the companies inter-se is liable to tax

Yes. In terms of Section 87(1) of the CGST Act, 2017, the supplies between the
companies inter-se for the period starting from effective date and ending with the date of order of the Court is liable to tax and supply and receipt shall be included in the turnover of supply or receipt of the respective Companies.

(ICAI FAQ PUBLICATIONS 06-09-2017 Liability in case of amalgamation /merger of Companies : FAQ NO. 5)