Futurewei Technologies Huawei Technologies Cisco Systems This document describes the postcard-based on-path telemetry with packet marking (PBT-M) using an MPLS Network Actions (MNA) flag to support OAM in MPLS networks. The scheme uses a single flag bit carried in a Flag-Based Network Action Indicator (Opcode 1) of the MNA Sub-Stack as defined in RFC 9994. The document provides the solutions to address the requirements for applying PBT-M in MPLS networks.