Exiting Nafta and implementing tariffs or a border-tax system would drive up U.S. car costs and put thousands of supplier jobs at risk, not stimulate auto-making like President Donald Trump hopes, according to a Boston Consulting Group study. In a report released Wednesday, the consultant estimated added costs to the U.S. auto sector from two policies being considered by Washington lawmakers: withdrawing from the North American Free Trade Agreement and introducing tariffs instead, or adopting a so-called border-adjusted tax. Either scenario would be costly, BCG found, with a 35 percent tariff on Mexican parts driving up U.S. auto-making costs by an average of $1,145 per car, and a 20 percent BAT adding $1,800. The added manufacturing costs—which could be as high as $27 billion a year if a 35 percent tariff replaces Nafta—may not cut into auto sales, said Xavier Mosquet, senior partner for BCG, which conducted the study for a partsmaker trade group. However, they would likely cause buyers to opt for fewer options, especially advanced electronics, to keep ballooning monthly payments down. Many of those parts, including rear-view cameras and automatic braking systems, are made in the U.S., putting an estimated 50,000 jobs at risk. BCG studied a variety of auto parts to look at the cost savings of making them in Mexico to see if the taxes—either a BAT or large tariff—would give manufacturers incentive to bring work back to the U.S. They won’t, Mosquet said, citing the disparity in labor costs. The parts would still be made in Mexico, but they’d cost more. “The value of cheap labor in Mexico far exceeds the cost of the taxes,” Mosquet said in an interview. “Most part suppliers will tell you the same story: They would take the cost of the tax.” Mosquet said tariffs on parts would have to get to about 50 percent to make parts firms bring work back. The BCG study was commissioned by the Motor & Equipment Manufacturers Association, a trade group representing parts suppliers. The group has been in contact with members of the House of Representatives, the Senate and the Trump Administration, said Ann Wilson, the association’s senior vice president of government affairs. Talks between the U.S., Mexico and Canada to revamp Nafta are expected to begin as early as Aug. 16.