may not consider a proposal that is not accompanied by a bond with security or certified check in the amount of $5,000, guaranteeing that the bidder if his proposal is accepted, will enter into a formal contract with the United States to furnish the paper or envelopes specified. The Committee may not consider a proposal from a person unknown to it unless accompanied by satisfactory evidence that he is a manufacturer of or dealer in the description of paper or envelopes proposed to be furnished.