(Adds Aprosoja quote, paragraph 6)
SAO PAULO, Nov 9 (Reuters) - Soybean growers in Mato Grosso, Brazil's largest producing state, have asked a court to cancel Monsanto's Intacta RR2 PRO patent claiming irregularities, including the company's alleged failure to prove it brings de facto technological innovation.
The Mato Grosso branch of Aprosoja, the association representing the growers that filed the lawsuit at a federal court on Wednesday, claimed "the patent does not fully reveal the invention so as to allow, at the end of the exclusivity period, any person can freely have access to it."
That requirement "avoids that a company controls a technology for an undetermined period of time," Aprosoja said, adding Intacta's patent protection extends through October 2022.
Monsanto said it has not been formally notified of the lawsuit and therefore would not make a statement.
Mato Grosso farmers are leading a push in Brazil to replace genetically modified soybeans with non-GM seeds.
"Aprosoja is not against innovation or paying for intellectual property," its head Endrigo Dalcin said, but added that farmers should not have to pay for technology that is protected by what it claims to be an invalid patent.
With about 53 percent of Brazil's soy area planted with Intacta technology in the 2016/17 crop cycle, Monsanto is a dominant force, Aprosoja says, citing data from consultancy Agroconsult.
Some 40 percent of the country's area is grown with Monsanto's Roundup Ready seed technology and only 7 percent is non-GM, the data showed.
This is the second time Mato Grosso farmers have challenged Monsanto in Brazil, its most important market outside the United States. In 2012, Aprosoja claimed Monsanto was charging royalties over a patent that had expired two years prior.
By 2013, after legal disputes, Monsanto had stopped collecting royalties linked to its first-generation Roundup Ready technology, Intacta's predecessor, according to Aprosoja. At that point, some farmers agreed to a discount rate on using Monsanto's newer Intacta seeds for four years, it said.
Monsanto, which is being acquired by Bayer AG, is also facing close scrutiny from regulators concerning that deal.
As one condition for approval in Brazil, Aprosoja's national branch is seeking to persuade local competition watchdog Cade to force the biotech company to sell its Intacta soy seed technology.
Biotech crops are genetically engineered to resist pests or disease, tolerate drought or withstand weedkillers such as glyphosate, the active ingredient in Monsanto's Roundup herbicide. (Reporting by Ana Mano; editing by Marguerita Choy and Jason Neely)