Comparison of the critical star formation surface density for cosmic-ray diffusion, given by Eq. (32), with the critical star formation rate to maintain the relation between star formation and magnetic field. Critical star formation surface densities are given as functions of the size of the star-forming region. We adopt here a characteristic rotational velocity of 20,40,and80 km s^-1, and explore values of the disk scale height of 0.5,1,and2 kpc. The highest critical values can be obtained for more compact star-forming regions. The relative importance of both processes is found to sensitively depend on the two quantities. We note that the critical star formation rate for cosmic-ray diffusion implicitly assumes observations at 1 GHz, while higher-frequency observations will probe more energetic cosmic rays, potentially implying a higher critical star formation rate.