The local gauge invariance associated with covariance leads to
first class constraints which remove
degrees of
freedom, albeit in phase space. For global symmetries such as Lorentz invariance, there is no first-class constraints associated
with them, and that global symmetry only removes
degrees of freedom. Technically, the counting should be
performed in phase space, but the results remains the same. See Section 7.1 for a more detailed review on the counting of
degrees of freedom.