Battling the government of Peru over an inactive metal smelter in one of the most polluted places on earth, billionaire Ira Rennert’s Renco Group hired eight former government officials from five lobbying firms in a span of 82 days since November.

Renco signed up a former member of Congress, a former trade official, former congressional staffers and a campaign manager for a high-ranking Senate Republican to plead its case in Washington. In a little less than two months of lobbying, two of those firms have reported receiving $225,000 in fees while attempting to enlist Congress and the Obama ...