21st Century IRS Act This bill amends the Internal Revenue Code to establish requirements for the Internal Revenue Service (IRS) regarding cybersecurity, the protection of taxpayer identities, information technology, and electronic systems. With respect to cybersecurity and identity protection, the bill: requires the IRS to work with the public and private sectors to protect taxpayers from identity theft refund fraud, requires the Electronic Tax Administration Advisory Committee to make recommendations to prevent identity theft and refund fraud, authorizes the IRS to participate in an information sharing and analysis center for identity theft tax refund fraud, and prohibits the disclosure of returns or return information to contractors or other agents for agencies that do not comply with confidentiality safeguards. The IRS must develop and implement: online accounts to provide services to taxpayers and return preparers, a process for accepting electronic tax forms and supporting documents, an Internet platform for Form 1099 filings, a fully automated program for disclosing taxpayer information for third-party income verification using the Internet, and uniform standards and procedures for the acceptance of electronic signatures. The bill also: establishes the position of IRS Chief Information Officer; limits redisclosures and uses of tax return information by individuals designated by taxpayers to receive the information; allows the IRS to require additional taxpayers to file returns electronically; and allows the IRS to pay fees for the use of credit, debit, or charge cards for tax payments if the fees are recouped by charging taxpayers.