Add to ORKGAutomated law enforcement systems support privately-operated enforcement bots to take legal action in hundreds of millions of cases a year. In the area of copyright, legal scholars have hypothesized the existence of “chilling effects” that harm public discourse by influencing people to self-censor protected speech. We test this hypothesis in a large-scale quasi-experiment with 9,818 accounts on Twitter that made 5,171,111 tweets. In a confirmatory interrupted time-series analysis, we find evidence that people reduce how much they post online after receiving a take-down notice from a copyright enforcement bot. On average, accounts sent fewer tweets after enforcement (p\u3c0.001). Accounts also changed from a daily increase in public tweets t...