In order to insure collection of tax, withholding is required by the person paying the income, rather than the one receiving it, in general and in the case of payments to nonresident aliens of fixed or determinable annual or periodical income from sources within the United States. [Estate of Bloch v. Commissioner, 44 T.C. 815, 819 (1965); citation and fn. ref. omitted.] Petitioner contends that it is not liable for withholding taxes because it is not a withholding agent under section 1441(a).