  We show that a suitable weak solution to the incompressible Navier-Stokes
equations on ${\mathbb{R}^3\times(-1,1)}$ is regular on
$\mathbb{R}^3\times(0,1]$ if $\partial_3 u $ belongs to $M^{2p/(2p-3),\alpha }
((-1,0);L^p (\mathbb{R}^3 ))$ for any $\alpha >1$ and $p\in (3/2,\infty)$,
which is a logarithmic-type variation of a Morrey space in time. For each
$\alpha >1$ this space is, up to a logarithm, critical with respect to the
scaling of the equations, and contains all spaces $L^q ((-1,0);L^p
(\mathbb{R}^3 ))$ that are subcritical, that is for which $2/q+3/p<2$.
