No contract for furnishing supplies to the Postal Service shall be made with any person who has entered, or proposed to enter, into any combination to prevent the making of any bid for furnishing such supplies, or to fix a price or prices therefor, or who has made any agreement, or given or performed, or promised to give or perform, any consideration whatever to induce any other person not to bid for any such contract, or to bid at a specified price or prices thereon.

Whoever violates this section shall be fined under this title 1

or imprisoned not more than one year, or both; and if the offender is a contractor for furnishing such supplies his contract may be annulled.