WASHINGTON — The government says it will raise by 25 percent the fines it will levy against employers who knowingly hire illegal immigrants. Attorney General Michael Mukasey and Homeland Security Secretary Michael Chertoff announced the increase, which is the first boost in fines in nearly a decade. Immigration and Customs Enforcement, the federal agency responsible for investigating illegal hirings, has stepped up its enforcement of the employer sanctions law in the past year, leading to a dozen major busts. Currently, fines range from $2,000 to $10,000 depending on the offense. The agency says some penalties could include at least six months in jail.