  We study the large-scale magnetic field structure and its interplay with the
gas dynamics in the Monoceros OB1 East molecular cloud. We combine observations
of dust polarised emission from the Planck telescope and CO molecular line
emission observations from the Taeduk Radio Astronomy Observatory 14-metre
telescope. We calculate the strength of the plane-of-the-sky magnetic field
using a modified Chandrasekhar-Fermi method and estimate mass over flux ratios
in different regions of the cloud. We use the comparison of the velocity and
intensity gradients of the molecular line observations with the polarimetric
observations to trace dynamically active regions. The molecular complex shows
an ordered large-scale plane-of-the-sky magnetic field structure. In the
Northern part, it is mostly orientated along the filamentary structures while
the Southern part shows at least two regions with distinct magnetic field
orientations. We find that in the Northern filaments the magnetic field is
unlikely to provide support against fragmentation at large scales. Our analysis
reveals a shock region in the Northern part of the complex right in-between two
filamentary clouds which were previously suggested to be in collision.
Moreover, the shock seems to extend farther towards the Western part of the
complex. In the Southern part, we find that either the magnetic field guides
the accretion of interstellar matter towards the cloud or it was dragged by the
matter towards the densest regions. The large-scale magnetic field in Monoceros
OB-1 East molecular clouds is tightly connected to the global structure of the
complex and, in the Northern part, it seems to be dominated by gravity and
turbulence, while in the Southern part it influences the structuring of matter.
