This file photo shows the U.S. Supreme Court Building in Washington, D.C.

The Supreme Court has sustained Monsanto Co.'s claim that an Indiana farmer violated the company's patents on soybean seeds that are resistant to its weed-killer.

The justices, in a unanimous vote Monday, rejected the farmer's argument that cheap soybeans he bought from a grain elevator are not covered by the Monsanto patents, even though most of them also were genetically modified to resist the company's Roundup herbicide.

Justice Elena Kagan says a farmer who buys patented seeds must have the patent holder's permission.

Monsanto has a policy to protect its investment in seed development that prohibits farmers from saving or reusing the seeds once the crop is grown. Farmers must buy new seeds every year.