That’s showing IRS who’s boss. They issue regulations saying you can’t do that. CPA tells client to go ahead and do it anyway.

§ 301.6109–4 IRS truncated taxpayer identification numbers.

(a) In general—Definition. An IRS truncated taxpayer identification number (TTIN) is an individual’s social security number (SSN), IRS individual taxpayer identification number (ITIN), IRS adoption taxpayer identification number (ATIN), or IRS employer identification number (EIN) in which the first five digits of the nine-digit number are replaced with Xs or asterisks. The TTIN takes the same format of the identifying number it replaces, for example XXX–XX–1234 when replacing an SSN, or XX–XXX–1234 when replacing an EIN. . . .

(b) (iv) A person may not truncate its own taxpayer identifying number on any statement or other document that it furnishes to another person. For example, an employer may not truncate its EIN on a Form W–2, Wage and Tax Statement, that the employer furnishes to an employee; and a person may not truncate its TIN on a Form W–9, Request for Taxpayer Identification Number and Certification.