20 CFR 209.4: Method of filing.

Any report or information required to be furnished under this part shall be prepared in accordance with instructions of the Board and shall be filed with the Board electronically, which includes the use of magnetic tape, computer diskette, electronic data interchange, or on such form as prescribed by the Board. If not filed electronically, reports shall be transmitted by facsimile or mailed directly to the Board. Any report which includes, or should include, information for 250 or more employees must be filed electronically, as described in this section.