Navistar International Corp., manufacturer of trucks and engines, said it will offer buyout packages to its U.S. salaried employees. Navistar, based in Lisle, Ill., confirmed to the Chicago Tribune Wednesday it told employees about buyout offers last week and that it can\'t determine what costs or savings the offer will bring. \"We currently do not know how many, if any, of the eligible participants will choose to participate in the [voluntary separation package] nor how many will be accepted,\" the company said in a statement. In a Security and Exchange Commission filing, the company said involuntary layoffs were possible. Navistar Spokeswoman Karen Denning said the company employs 6,300 salaried workers in the United States. Hourly workers are not part of the buyout program. Denning declined to tell the Tribune the company\'s reduction goal. In 2010, Illinois offered Navistar $64.7 million worth of incentives, including an estimated $63.9 million in tax credits over 10 years and $750,000 in training funds, the Tribune said. In exchange, the company promised to add at least 400 jobs, retain 2,200 workers and invest $205 million in the state. In 2010, Navistar employed about 3,100 full-time workers in Illinois. Denning said Navistar did not receive any incentives in 2011 but will continue to meet its agreed-to employment levels. The announcement came a week after Navistar said it reached agreement with a competitor to meet 2010 federal engine emission standards and revealed it faced an SEC investigation \"related to certain accounting and disclosure matters.\" Navistar has said it is cooperating with the SEC investigation.