Paraphrased from pre-2018 Pub 525-

If your employer provides you with a product or service and the cost of it would have been allowable as a business deduction if you paid for it yourself, the cost isn't included in your income.

Client questions why the value of employer-provided uniforms is now appearing on 2018 payroll. Net pay is reduced because of the consequent tax withholding. (Hes employed by county government.)

He asked what changed.

My attempted explanation:
Since employee business expenses will no longer be deductible, thus not meeting the test to be excluded from wages, those employer-paid fringe benefits are now included as taxable wages.

So should employees now see certain fringe benefits included in wages? Examples- Certifications, tools, uniforms, malpractice insurance premiums, trade magazines (such as described in the Pub 525 example where this is discussed under Working Condition Benefits)?