The penalties are for not paying the 941 tax on time according to the payment schedule, which depends on the amount of tax. Small companies may be required to pay only quarterly or monthly, but larger companies have payments due within 3 business days after every payroll. The penalties depend on how late the payments are, bit they go up rapidly, and can be 100% if there is no payment.There is often no penalty for not filing the 941 on time if the payments have been made, but the IRS will be sending you a lot of mail to get it filed.