Consider two point charges in space: one positive(+Q) and other negative(-Q), lying on the y-axis and separated by distance 'r'. In frame A, both charges are at rest so, only attractive electrostatic force (F_elec) acts on both the charges which is defined by coulombs formula. In another frame B, both charges are moving with velocity 'v' in positive x-direction so forces acting on the charges are attractive electrostatic force(F_elec) and repulsive magnetic force(F_mag). It can be seen that the net attractive forces acting on the charges is greater in frame A than in frame B by an amount F_mag since, F_elec is same in both frame A & B. Also, F_mag = - F_elec ,when v=c [this result can be obtained by using coulomb law, ampere law, and the fact that epsilon*mew=1/(c^2)] Conclusion : So an observer in frame B will see that net attractive force acting on charges is reduced than in frame A. Also, the net attractive force in frame B tends to zero as 'v' approaches 'c'. Q: How is the above situation compatible with SR. SR says nothin about relativity of forces only about relativity of length and time.