Not every issue is a Federal vs States issue. Your question applies only to whether or not the federal government has the "right" to stop this, not whether it is good for this to happen.
• Tag lambs for slaughter close to the point of dispatch from the farm, since the acute pain of tagging and transporting is less than the chronic pain associated with infected ears and retagging.
• Don’t leave the tagging of store or breeding lambs to the day the lambs leave the farm. Try to do it weeks before. Lambs travelling with bleeding ears will be stressed and liable to infection. Also, although the flystrike period may have ended on the farm where they were tagged, lambs may be transported to warmer regions where flystrike can then become a problem.
• Restrain the lamb firmly between your legs or in a similar secure position. Do not tag lambs over the edge of the race - they may jump, leaving a split ear.
• The baseline tag should be inserted at least onethird away from the head along the underside of the sheep’s left ear. Insert tags with the male part pushed through from the back of the ear.
• Use clean tags and taggers. To avoid infection keep the tags dry in a box before use. Do not apply wet disinfectant to the ear or any gels as free air movement stops festering.
• Apply tags under hygienic conditions, not on a wet day or if the lambs are dirty.
• You may consider using an insect repellent/topical insecticide on the animal but it is important to comply with instructions for any products used so that the regulations regarding health and safety and withdrawal periods are met. Also check that any chemicals used do not remove the writing on the tag.
• Do not tag diseased lambs or lambs showing signs of Orf (scabby mouth).
• Several different designs of tag are available and it is important to look at the manufacturer’s instructions for each type of tag. It is also important to allow for ear growth when fitting loop tags, but leaving too much room leads to problems with festering ears.
• Do not tag through the cartilage ridge as this can result in a dropped ear. Look for and avoid obvious blood vessels in the ear.
• Keep tags in a secure, safe, clean place and don’t give them to anyone else.
• When putting the second tag in the ear, place it close enough to the head so that enough room is left on the outside for another tag.
• Lambs which have lost their original tags, and the holding of birth is not known, are tagged with a red replacement tag.
• For lambs with very thin ears, there is slightly more muscle in the front edge of the ear and this position has been used for tagging, but when doing this avoid tag types that can be flicked into the eye.