Keeping your time sheets accurate is important for being perceived as honest and reliable. In most cases, you can be fired for incorrect time sheets. Whether or not you'll actually be terminated depends on your employer's policies as well as whether the inaccuracy was accidental or deliberate.
Employment Contract Guidelines
If you have an employment contract, your contract addresses the specific circumstances in which you can be fired. Even if your contract doesn't mention time sheet inaccuracies, such inaccuracies might be covered under clauses that address deception, fraud or insubordination. If your contract establishes specific procedures that must be followed before you can be terminated -- such as a warning or a last-chance agreement -- then your employer has to follow this protocol before terminating you.
At-Will Employment States
If you don't have a contract, state law governs whether or not you can be fired. Every state except for Montana has at-will employment laws, which means you can be fired for almost any reason -- or for no reason at all. Your employer is only prohibited from firing you if the reason for termination is discriminatory or if you are a whistleblower. Employers are also prohibited from terminating employees in retaliation for filing a complaint or lawsuit, or for exercising basic employment rights, such as the right to take family and medical leave.
Falsifying Time Sheets
If you deliberately falsify your time sheets, your employer can fire you in most cases. Such an act is a form of criminal fraud, and can subject you both to prosecution and civil lawsuits. This means that, if you've already been paid, your employer could fire you and then sue you to recover the money you didn't actually earn.
Will You Be Fired?
It's possible to make mistakes on your time sheets by entering the wrong day or time or forgetting to clock in or out. Most employers understand these mistakes, but you'll need to rectify the error as soon as you notice it. If you have a pattern of routinely submitting incorrect information -- even accidentally -- your employer might still discipline or terminate you, since such behavior could signal that you're irresponsible in other ways, too.