  Globular clusters (GCs) associated with the Sagittarius dwarf spheroidal
galaxy (Sgr dSph) have evolved under the gravitational potential of both Sgr
dSph and the Milky Way. The effects of these potentials are most pronounced in
the extra-tidal regions as compared to the central regions of the GCs.We aim to
study the extra-tidal regions of the GCs that are possibly associated with Sgr
dSph, namely Arp 2, Terzan 8, NGC 5634, NGC 6284, Terzan 7, NGC 2419, NGC 4147,
M 54 and Pal 12, using data from the {\it Gaia} early data release 3. We
selected the extra-tidal candidates based on their angular distances from the
cluster centre in the RA-Dec plane, proper motions of the clusters and the
individual extra-tidal star candidates, and their positions on the
colour-magnitude diagrams of the clusters. We found extra-tidal candidates for
the nine studied GCs. For eight of them, the surface density of candidate
extra-tidal stars in the vicinity of the clusters is in significant excess with
respect to more distant surrounding fields. No extended extra-tidal features
beyond 5 tidal radii were detected for any of the clusters. We publish a list
of the most probable extra-tidal candidates that we determined using Gaia
astrometric and photometric data. Our analysis shows that the clusters that are
associated with Sgr dSph are more likely affected by the gravitational
potential of the Sgr, as the distribution of extra-tidal stars is elongated in
the same direction as the local stream. NGC 4147 is the only exception. We
found some high-probability candidate extra-tidal stars in several of the
analysed clusters. We failed to detect any coherent large-scale tidal tail
around them.
