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The request is one of several conditions outlined to potential buyers wishing to access the Light data room, Cemig said in a securities filing.
Interested firms should also be present in Brazil's electricity distribution or generation segments with at least 2mn consumers or 1GW of installed capacity.
Meanwhile, financial investors must have assets under management with a net value of at least US$5bn.
According to Cemig, which is controlled by Minas Gerais state government, the data room contains information designed to "assist potential investors in preparation for non-binding proposals."
The company previously announced that potential buyers would have access to the data room for 30 days, pending the signing of a confidentiality agreement.
The sale forms part of a 9bn-real (US$2.7bn) divestment program launched by Cemig in June.
In July, the company said it had received 12 expressions of interest for the stake, which has a book value of 2.06bn reais.
Light's power generation assets include five hydroelectric plants with combined installed capacity of 855MW. The company is also Rio de Janeiro's largest power distribution concessionaire, providing electricity to around 4mn consumers.
More information, in Portuguese, can be seen here.