For the past two years, Andy Techmanski ran a tiny family utility-contracting company out of his home in the ski town of Whitefish, Mont., getting relatively modest jobs out West. They helped rebuild a fire-ravaged power line in mountainous Washington State and are in the process of supplying a transformer to a Montana electric cooperative.

But now, Mr. Techmanski and his father-and-son firm, Whitefish Energy, are drawing widespread attention and congressional scrutiny for an outsized deal half a world away: a $300 million contract with the Puerto Rico Electric Power Authority to rebuild 100 miles of power transmission lines across the island’s shattered electric grid.

“We just answered the call,” Mr. Techmanski said in an interview from Puerto Rico. “We got on a plane and came over here right after.”

The size of the contract and the scale of the job awarded to a company that had just two full-time employees is now raising questions about how Puerto Rico’s bankrupt power authority awarded contracts and reached out for assistance in the chaotic days after Hurricane Maria, which snapped utility poles like Popsicle sticks and tore down hundreds of miles of power lines.