A method for forming a passivation layer on a strip of packaging steel provided with a at least one tin-plated surface for forming a tin-oxide layer on said tin-plated surface to provide excellent sulphide staining resistance of the strip of packaging steel, for producing a packaging container or a can for packaging food, said method comprising the steps of: - subjecting said tin-plated surface to an anodic treatment at a pH of from 8 to 11.5 in a suitable aqueous electrolyte, wherein the suitable electrolyte is a phosphate solution, borate solution, sulphate solution or a carbonate solution wherein the electrolyte for the anodic treatment does not contain mono-atomic halogen anions (Group 17) such as Cl -, F - - wherein the thickness of the tin oxide layer, expressed in Coulomb/m 2 and representing the total charge needed to reduce the layer to metallic tin is related to anodic treatment time (t), current density by D = E x A x t, where E is the efficiency of the electrochemical reaction, and wherein D is at least 30 C/m 2 and at most 100 C/m 2; - wherein the electrolyte comprises monoatomic cations from Group 1 or 2 from the periodic table or polyatomic cations, and polyatomic anions; - said electrolyte not comprising a watersoluble silicate of composition M 2 O·nSiO 2, wherein M is an alkalimetal-ion or a quaternary Ammonium-ion and n is a natural number between 0.8 and 7; - wherein the anodic treatment is performed in an industrial tinning line running at a line speeds in excess of 300 m/min; - wherein the anodic treatment is performed in-line with or immediately after electrolytic tinning, and wherein the anodic treatment time (t) is at most 5 seconds; - optionally rinsing and drying the anodically treated tin-plated surface - subjecting the anodically treated tin-plated surface to a chemical passivation treatment free from using hexavalent chromium compounds - drying of the passivated anodically treated tin-plated surface - final processing such as oiling, winding, cutting etc. - subjecting said tin-plated surface to an anodic treatment at a pH of from 8 to 11.5 in a suitable aqueous electrolyte, wherein the suitable electrolyte is a phosphate solution, borate solution, sulphate solution or a carbonate solution wherein the electrolyte for the anodic treatment does not contain mono-atomic halogen anions (Group 17) such as Cl -, F - - wherein the thickness of the tin oxide layer, expressed in Coulomb/m 2 and representing the total charge needed to reduce the layer to metallic tin is related to anodic treatment time (t), current density by D = E x A x t, where E is the efficiency of the electrochemical reaction, and wherein D is at least 30 C/m 2 and at most 100 C/m 2; - wherein the electrolyte comprises monoatomic cations from Group 1 or 2 from the periodic table or polyatomic cations, and polyatomic anions; - said electrolyte not comprising a watersoluble silicate of composition M 2 O·nSiO 2, wherein M is an alkalimetal-ion or a quaternary Ammonium-ion and n is a natural number between 0.8 and 7; - wherein the anodic treatment is performed in an industrial tinning line running at a line speeds in excess of 300 m/min; - wherein the anodic treatment is performed in-line with or immediately after electrolytic tinning, and wherein the anodic treatment time (t) is at most 5 seconds; - optionally rinsing and drying the anodically treated tin-plated surface - subjecting the anodically treated tin-plated surface to a chemical passivation treatment free from using hexavalent chromium compounds - drying of the passivated anodically treated tin-plated surface - final processing such as oiling, winding, cutting etc.