Exploiting large cross-sectional variation in exposure to securities losses across euro area banks, we show that banks more negatively exposed to the July 2022 monetary policy tightening lost access to the interbank market and cut lending, irrespective of whether the securities were booked at market or historical value. Importantly, banking groups provide liquidity to domestic subsidiaries, reducing the impact of their security losses on corporate lending, but foreign subsidiaries of banking groups and stand-alone banks with more significant securities losses reduced lending to corporate borrowers to a larger extent. Our results show how differences in banking structure can contribute to an uneven transmission of monetary policy.