Go to the IRS or see a tax law lawyer right away. Yes, it may affect his career. Punishment is up to the courts and depends on a wide variety of factors. No way to really tell without knowing a whole lot more.
This answer is for general purposes only and does not establish an attorney-client relationship. The law in your state may differ and your best answer will always come from a local attorney that you meet with privately. For a Free Online 50 State National List of Consumer Law Lawyers, click on this link (http://tinyurl.com/79ku5jx) and find one near you
It is a violation of the law to knowingly provide the IRS with false information. Without knowing more about your specific situation it's hard to say what his punishment may be but it may have a negative impact on his career.