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% replaces any number of letters (la% - lake, lamp)_ replaces one letter (ca_ - car, cat)

Crossword clues for The IRS requires them 4 letters:

SSNS: IRS requirements
SSNS: The IRS requires them
EFILE: IRS requirement, often
EFILE: IRS requirement for many
SSN: IRS requirement
TAXIDNUMBER: Business datum required by the IRS