3. The law may define basic sectors in which private enterprises and other entities of the same nature are forbidden to do business. Article 87 (Foreign economic activity and investment) The law shall discipline economic activity and investment by foreign natural and legal persons, with the aim of ensuring that they contribute to the country’s development and defending national independence and workers’ interests. Article 88 (Abandoned means of production) 1. Abandoned means of production may be expropriated under terms and conditions to be laid down by law, which must pay due regard to the specific situation of the property of emigrant workers. 2. Means of production that are abandoned without good reason may also be the object of compulsory rental or operating concessions under terms to be laid down by law. Article 89 (Worker participation in management) The workers of units of production in the public sector shall be ensured an effective participation in the respective management. TITLE II Plans Article 90 (Objectives of plans) The objective of economic and social development plans shall be to promote economic growth, the harmonious and integrated development of sectors and regions, the just division of the national product between persons and between regions, the coordination of the economic policy with the social, education and cultural policies, the defence of the rural world, the preservation of the ecological balance, the defence of the environment and the quality of life of the Portuguese people. Article 91 (Drawing up and implementation of plans) 1. National Plans shall be drawn up in harmony with the respective laws governing the Major Options, and may incorporate specific programmes with a territorial and sectoral scope.