This paper investigates whether large customers can influence the information environment of their supplier stock prices. We find that suppliers whose sales are concentrated on a few large customers have low stock price synchronicity, suggesting that their stock prices reflect firm-specific information well. We show that the negative effect of customer concentration on supplier stock price synchronicity is more pronounced when suppliers have weak bargaining power against their large customers. The instrumental variable regressions confirm the effect of customer concentration. We also find that stock prices of suppliers with high customer concentration reflect less market-wide information and more firm-specific private information, consistent with their low price synchronicity. To support that private information is the main driver of low price synchronicity, we show that there is significantly more insider trading and analyst divergence for suppliers with high customer concentration.