More than 10 Allowances

I've heard that it is illegal to claim more than 10 allowances. Is that true?

Note that it is legal to claim more than 10 withholding allowances, but the IRS does require that employers notify them of employees who claim more than 10 withholding allowances on their W-4.

Note:We have heard of one client contacted by the Oregon Department of Revenue. They were asked to justify the number of allowances they were claiming. A copy of the printout was sufficient for the explanation.