  Detailed spectropolarimetric studies may hold the key to probing the
explosion mechanisms and the progenitor scenarios of Type Ia supernovae (SNe
Ia). We present multi-epoch spectropolarimetry and imaging polarimetry of SN
2019ein, an SN Ia showing high expansion velocities at early phases. The
spectropolarimetry sequence spans from $\sim -11$ to $+$10 days relative to
peak brightness in the $B$-band. We find that the level of the continuum
polarization of SN 2019ein, after subtracting estimated interstellar
polarization, is in the range $0.0-0.3\%$, typical for SNe Ia. The polarization
position angle remains roughly constant before and after the SN light-curve
peak, implying that the inner regions share the same axisymmetry as the outer
layers. We observe high polarization ($\sim 1\%$) across both the Si II
$\lambda6355$ and Ca II near-infrared triplet features. These two lines also
display complex polarization modulations. The spectropolarimetric properties of
SN 2019ein rule out a significant departure from spherical symmetry of the
ejecta for up to a month after the explosion. These observations disfavour
merger-induced and double-detonation models for SN 2019ein. The imaging
polarimetry shows weak evidence for a modest increase in polarization after
$\sim 20$ days since the $B$-band maximum. If this rise is real and is observed
in other SNe Ia at similar phases, we may have seen, for the first time, an
aspherical interior similar to what has been previously observed for SNe IIP.
Future polarization observations of SNe Ia extending to post-peak epochs will
help to examine the inner structure of the explosion.
