SAO PAULO, Sept 19 (Reuters) - Brazilian steelmaker Usiminas plans to file a petition with antitrust watchdog CADE against a recent decision allowing its rival Companhia Siderurgica Nacional (CSN) to hold a stake higher than 5% in the company.

CSN had been mandated by CADE in 2014 to sell the 17% stake it owned then in Usiminas within five years. In 2019, CSN got an extension of three more years to complete the sale.

As the second deadline approached in 2022, CSN once again asked for a waiver, and this time CADE superintendent Alexandre Barreto decided there was no more need of selling the stake, as long as CSN does not vote in shareholders assemblies.

CSN has sold part of the stake over the years and currently holds 12.9% of Usiminas capital, according to B3 data. CSN owns 15.1% of Usiminas' common shares and 10% of preferred capital.

Usiminas plans to file a petition with CADE against the decision, alleging a decision by the superintendent alone could not reverse a former decision voted by all CADE councilors, according to two people with knowledge of the matter.

The company also plans to allege that over the years, CSN has not acted as a passive investor and that CADE decisions have given excessive time to CSN to divest, the people added, asking for anonymity because are not authorized to discuss the matter publicly.

CSN did not immediately comment on the matter. CADE and Usiminas declined to comment.

(Reporting by Tatiana Bautzer Editing by Marguerita Choy)