SAO PAULO (Reuters) -Brazilian competition authority CADE has ordered soybean traders in the world's largest soybean exporter to end a program called "Soy Moratorium" or face hefty fines, according to a decision signed by General Superintendent Alexandre Barreto de Souza on Monday.

In the ruling seen by Reuters, De Souza recommended a full-blown investigation into the signatories of the voluntary program, which bars soybean traders from buying the oilseed from farmers who cleared land in the Amazon rainforest after July 2008.

The two-decade-old voluntary agreement seeks to protect the Amazon rainforest. Brazilian farmers have complained that the agreement blocks farmers who comply with environmental rules.

Companies and trade groups Anec and Abiove, which represent global grain handlers such as ADM, Bunge, Cargill, Louis Dreyfus and Cofco, have 10 days to comply, according to the document.

Anec, which represents grain exporters, said CADE's stance in relation to the soy moratorium is "extremely worrisome." It said it will take administrative measures to appeal the decision.

The soy moratorium should stand as it is "a multi-sector pact" backed by civil society, the Ministry of the Environment and Brazilian Environment agency Ibama, Anec said.

Abiove, which represents oilseeds crushers, said it was "surprised" with De Souza's decision to recommend a full-blown probe and impose preventive measures, and said it would take measures to defend the legality of the soy moratorium program.

CADE's preventive measure must be observed by the soy moratorium's working group, including Anec and Abiove, and exporting firms that are signatories of the program, according to De Souza's decision.

Under the order, soy exporters are to refrain from collecting, sharing, storing and disseminating commercially sensitive information related to the soy trade and the farmers they do business with.

The preventive measure also calls for the withdrawal of all soy moratorium information and related online publicity.

CADE's General Superintendent wrote that companies that wish to apply soy moratorium criteria to buy soybeans grown in the Amazon "must do so independently and in accordance with national legislation."