Google Forms now have a limit to one answer by respondent. It requires that the user sign-in using a Google account. For details see the official help article: Send your form to people
In certain situations you could be 100% sure that the employees will only be able to submit one response in other you should measure the risks and evaluate the use of Google Forms considering them.
If the form owners organization has G Suite, they could ask the organization administrator if there are individuals with more than one account. In small organizations it's very rare that an individual has more than one account, I think.
If the form owners are using consumer accounts (usually they have an gmail.com email address) you should know the employees to properly evaluate the probabilities of having more than one response by employee.