Wigner showed that irreducible representations of the Poincare group can be listed, depending of the mass being zero or larger then zero, as $2J+1$ dimensional representations where $J$ is half-integer (for mass non-zero, positive) and just 2 dimensional for mass zero.
Now, if we have four-vector or more generally, tensor, representation, we can decompose 4d vector representation into 1d spin 0 and 3d spin 1 representation.
Now, when talking about particles, we define fields which determine specific properties of particles. In order to describe particles we try to introduce spin representation together with vector representation. So for spin 1 we define a condition which defines so called polarization vectors and we end up with three of them. Now, under Poincare transformations, am I to assume that these 3 basic vectors transform among themselves under the Poincare group in vector representation?
So, to conclude, can we define transformations of spin 1 field as vector ones? And are we to define transformations of spin 1/2 particles as not vector because with spin 1/2 the components do not transform as vectors? And, for spin 1, these 3 polarization vectors, do they define or constrain, directions of the field?