The Roth 401(k) is a type of retirement savings plan. It was authorized by the United States Congress under the Internal Revenue Code, section 402A, and represents a unique combination of features of the Roth IRA and a traditional 401(k) plan. Roth 401(k) contributions are irrevocable-once money is invested into a Roth 401(k) account, it cannot be moved to a regular 401(k) account. 2  Employees can roll their Roth 401(k) contributions over to a Roth IRA account upon termination of employment.