We examine the relation between information externalities along the supply chain and voluntary disclosure. Information transfers from a major customer's earnings announcement (EA) can substitute for its supplier's disclosure. Conversely, if the customer's EA increases uncertainties regarding the supplier's future prospects, it can increase the demand for disclosure. After controlling for information incorporated in supplier returns, we find that the supplier is more likely to issue earnings guidance after the customer's EA when the EA news deviates more from the market's expectation. The positive effect of the customer's news on earnings guidance is weaker when common investors, supply-chain analysts, or a common industry allow investors to better understand the value implications of the news, while the effect increases with the importance of the customer to the supplier. The effect is also stronger when EA news is negative rather than positive. Collectively, the results suggest that supply-chain relationships influence voluntary disclosure.