The Tata Group strongly denied the charge and said there had been no illegality at any point.
The decision, which will have many political implications in the state, was taken at a meeting of the state Cabinet. The two check dams are at the Anakkulam Lakshmi Tea Estate and the Chittuvare Estate, near the Kundala dam.
The government also decided to take 'strict action' against all illegal construction, including resorts and hotels, and land acquisitions in the Munnar area. All such construction will be demolished.
The decision follows a high court order to remove all such illegal construction to preserve the natural resources and beauty of Munnar.
A seven-member cabinet team lead by Kodiyeri Balakrishnan, home minister, had visited the area last week and given a report. The cabinet today approved all the 16 suggestions by the committee.
All land acquisition before 1977 will be made legal and title deeds to these alloted in a phased manner. The cabinet committee had said the Tatas had illegally acquired land, apart from the 58,000 acres leased to them for tea estates and other agricultural purposes.
Their report said the Tatas had also sold 1,000 acres in breach of the law, for constructing resorts.
The Tata Group denied all the allegations. T Damu, spokesperson for the Group, told Business Standard they had an agreement with the erstwhile Travancore government for using water resources for agriculture and domestic purposes, signed in 1928.
As allowed in the agreement, a check dam was constructed at the Chittuvare Estate for the use of the workers. The dam at Anakkulam was constructed by the British; the Tatas had only repaired the dam.
There was no illegal construction or violation of any lease agreement or any other law.
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