MANETs (mobile ad-hoc networks) are already starting to get deployed in tactical settings. In such networks, where capacity is limited compared to wired networks, QoS mechanisms are needed in order to serve high priority traffic with acceptable quality under both light and heavy load conditions. A crucial part of a QoS architecture is the admission control mechanism, making decisions on whether new flows may be admitted into the network based on the current traffic situation. The IETF is currently standardizing an architecture for admission control and flow termination for wired DiffServ domains, named Pre-congestion Notification (PCN). In this paper the possibility of applying the PCN mechanisms to wireless MANETs is studied. MANET specific challenges are discussed, as well as necessary modifications to the PCN mechanisms. Simulation results are presented, identifying the introduction of probing as a key measure in order to reduce the amount of signaling and to base admission decisions on fresh network status information.