Sir Edward Garnier suggested the RSPCA could use prosecutions as a political weapon, the Daily Mirror reported. He cited a case in Oxfordshire, close to the parliamentary constituency represented by Prime Minister David Cameron, where the group spent more than 300,000 pounds (about $500,000) making a legal case against the local hunt.
"It seems to me that if they continue to prosecute at such huge expense and in such a disproportionate way they will be open to public criticism," Garnier said.
A prominent lawyer who served as solicitor general from 2010 to 2012, Garnier said the RSPCA has a responsibility to investigate animal cruelty. But he said once the group has gathered information it should hand its evidence over to the Crown Prosecution Service.
An RSPCA spokesman said the group has no intention of taking Garnier's advice.
"We are as committed to our mission, to promoting compassion to all creatures and prevent cruelty, as ever," he said.
A Labor MP, Paul Flynn, suggested Garnier objects to the prosecution of those who are "rich, powerful and Tory." Attorney General Dominic Grieve said the right of groups and individuals to bring private prosecutions is "fundamental and important" in the British legal system.