Brief facts of the case are that in the year 1988 the State of Haryana formulated an industrial policy and certain industries, which were set up after 1.4.1988, were exempted from payment of sales tax on the goods manufactured by them. Since there was no express provision of exemption in the Haryana General Sales Tax Act, 1973 (for brevity, ‘the HGST Act’), therefore, with a view to augment industrial development in the respondent State, Section 13-B was inserted in the HGST Act vide Haryana Act No. 26 of 1988, inter alia, empowering the State of Haryana to exempt any class of industry from payment of sales tax on the goods manufactured by them. On 17.5.1989, the State of Haryana notified Haryana General Sales Tax (Second Amendment) Rules, 1989, amending the Rules. After Chapter IV of the existing Rules, Chapter IV-A was inserted with the heading of “Class of Industries, period and other conditions for exempting/deferring from payment of tax”. In the said chapter, Rule 28A has also been incorporated in the Rules. Rule 28A(2) of the Rules defines meaning of various expressions including ‘operative period’, ‘new industrial unit’, ‘eligible industrial unit’, ‘screening