The three independent magnetoelectric susceptibilities of GdA10, have been measured in the critical region 6)& 10 ' & hT/T"& 1 X 10 '. For all three elements, we find power-law behavior with the same critical exponent P = 0.31+0. 01. Although Gd+ is an S-state ion and the dominant interaction is isotropic Heisenberg exchange, this exponent is Ising-like. This is interpreted as being due to the strong uniaxial character of the magnetic order. Our results are compared with those for other magnetoelectric materials.