The IRS has posted a Frequently Asked Questions page regarding Electronic Filing ID Numbers.
Topics include what an EFIN is, who owns an EFIN, and the roles of authorized IRS e-file providers.
Other questions address how authorized IRS e-file providers can find out if an associated third-party provider has a valid EFIN, compromised EFINs and actions the IRS might take if an EFIN is compromised, as well as whether EFINs are transferable.
Invalid uses of an EFIN, according to the page, include if a preparer had an EFIN at a previous firm but moved to another firm, lack of use of an EFIN to e-file in the last two years, and possible changes in circumstances of EFIN use after the death of a person listed on the application.
The IRS e-file help desk also lists its phone number: (866) 255-0654, available 6:30 a.m. to 8 p.m. Central Time.