The semiempirical scaling law for flux pinning,Fp=ABnc2bl(1−b)mhas been tested for bronze process Nb3Sn conductors under uniaxial tension. The dependences of the bulk pinning forceFpon the upper critical fieldBc2 and the reduced field,b=B/Bc2, were weakly affected by strain. However, the factorA, which depends on the number and strength of the pinning centers, and on the Ginzburg‐Landau parameter &kgr; decreased by more than a factor of 20 when the compressive prestrain on the Nb3Sn was removed by application of external stress. The variations ofTcandBc2with strain suggest that the change in &kgr; is not sufficient to account for the change inA. Therefore, it is probable that strain induces microstructural changes which affect the number and/or strength of the pinning centers.