This is what IRS currently says.  However, the agreement that e-filers must sign states that IRS can change the rules without notice at any time:

IRS e-file Monitoring Visitations
The IRS monitors Providers through review of IRS records and during visits to Providers’ offices and other locations where Providers perform IRS e-file activities. During monitoring visits, the IRS may investigate
complaints and ensure compliance with IRS e-file rules. Monitoring may include, but is not limited to the following:
■ Reviewing the quality of IRS e-file submissions for rejects and other defects
■ Checking adherence to signature requirements on returns
■ Scrutinizing advertising material
■ Review records
■ Observing office and security procedures
■ Checking Tax Compliance on the Firm, Principals and Responsible Officials and pursuing non-compliance