(AP) — Facebook has shut down the personal accounts of a pair of New York University researchers and shuttered their investigation into misinformation spread through political ads on the social network.

Facebook says the researchers violated its terms of service and were involved in unauthorized data collection from its massive network. The academics, however, say the company is attempting to exert control on research that paints it in a negative light.

The NYU researchers with the Ad Observatory Project had for several years been looking into Facebook’s Ad Library, where searches can be done on advertisements running across Facebook’s products.