  In this work we study the entanglement properties under a Lorentz boost of a
pair of spin- 1 massive particles, with spin and momentum as the sole degrees
of freedom of the system. Different cases for entanglement between spins and
momenta are considered as initial states and it is shown that entanglement
between the different degrees of freedom is, in general, not invariant. We
analyze the entanglement change in terms of the Wigner rotation induced by the
transformation and show that, for the case of spin-1 particles, the relative
entanglement change between different states depends strongly on the boost
velocity.
