Do you have the authority to sign checks or pay bills for a business? Even if you are not an officer or owner of a business the IRS can attack you for the "withheld" taxes. Under Internal Revenue Code Section 6672, the IRS can make any
"responsible" person individually liable for the amount of money that should have been withheld in employees' paychecks and was not paid to the government.
This process is usually started by a Revenue Office (IRS collection agent) who issues a Notice of Finding of Responsibility. Most people ignore the letter thinking it will go away. If a challenge is not made within 90 days, the IRS will issue an assessment against the individual. The IRS will then file a Federal Tax Lien which is like a judgments and slams your credit score.
Even if one person is found "responsible" the IRS can still go after others. It is not a matter where you are only responsible for your share. Each person is 100% liable. The IRS can levy wages, take bank accounts and other assets.
In addition to civil penalties, the IRS sometime prosecutes people for failing to file or pay payroll taxes. THe IRS has announce a new push to file criminal as well as civil actions. Some struggling business owners spend many years in jail because they chose to pay the light bill to keep the business open and did not pay taxes.
This process is quite complex but can be fought if the matter is handled quickly by a good tax attorney.