Employers are required to withhold Social Security taxes, Medicare taxes, and income tax from employee wages. These are typically called withholding taxes or trust fund taxes because these funds always belonged to the IRS and were held by the employer in trust. Employers are required to submit the trust fund taxes to the IRS. Additionally, the employer needs to file with the IRS quarterly employment tax returns on Form 941 and annual unemployment tax returns on Form 940. The IRS aggressively enforces the collection of unpaid trust fund taxes along with interest and penalties. In addition to pursuing the employer, the IRS may assess the Trust Fund Recovery Penalty for the full amount of the trust fund taxes against company officers and responsible parties. The IRS has the power to shut down the business and liquidate the assets to pay the trust fund taxes. Furthermore, the IRS can criminally prosecute company officers and responsible parties who willfully fail to file employment tax returns or to pay the trust fund taxes of the employer.