According to Newton's law of viscosity,
$\tau=\frac{F}{A}=-\eta \frac{d v}{d z}$
As we know that viscous force acts like friction between the layer of two fluids due to which shearing action will occur, a shear force will always act tangential to the plane of the fluid/object. So, tangential stress will be generated between the two layers of the two fluids.