General Motors Co. is preparing for an initial public offering that may sell 20 percent of the Treasury’s stake in the automaker and reduce the U.S. to a minority owner, two people familiar with the plan told Bloomberg.

The aim is to sell a fifth of the government’s 304 million shares, said the people, who asked not to be identified revealing private discussions. That would reduce the Treasury Department’s stake to less than 50 percent from 61 percent now. Final decisions on which owners will sell how many shares haven’t been made and may change, the people said.

A registration statement may be filed in August, aiming for a November stock sale, said four people familiar with the plan. The sale will probably raise $10 billion to $15 billion, depending on the company’s performance, the strength of the economy and the health of the IPO market, the people said.

An August filing means Detroit-based GM could have the IPO ready around the time of the Nov. 2 congressional elections, said the people. If Treasury can sell enough shares, President Barack Obama could help other Democrats running for office by arguing that his administration’s restructuring of GM is paying off, said Joe Phillippi, president of AutoTrends Consulting.

“The government wants a successful offering soon so they can say that they took the company through bankruptcy, turned it over to independent management and are taking it public,” said Phillippi, who is based in Short Hills, New Jersey. “This would be part of the campaign spin.”