Vets4Pets in Bramley are treating two dogs that had been exercised in a recreational field on Broad Lane, near the Black Lion pub.
Posting on the practice's Facebook page, vets said:
"Two dogs have been brought in today after a walk in the field behind the Black Lion in Bramley, and it's likely they may have been poisoned.
"Please avoid the area and warn all dog and cat owners in the area. These dogs are both critically ill and in the veterinary hospital receiving around the clock care.
"Symptoms include vomiting, being unable to stand, collapsing, trembling and fitting. It is likely that food laced with poison has purposely been left in the area."