http://www.nrmp.org/res_match/policies/map_main.html#comm
6.0 Restrictions on Persuasion
One of the purposes of the Matching Program is to allow both applicants and programs to make selection decisions on a uniform schedule and without coercion or undue or unwarranted pressure.
Both applicants and programs may express their interest in each other; however, they shall not solicit verbal or written statements implying a commitment. Applicants shall at all times be free to keep confidential the names or identities of programs to which they have or may apply. In addition, it is a breach of the applicable Match Participation Agreement for:
(a) a program to request applicants to reveal ranking preferences; or
(b) an applicant or program to suggest or inform the other that placement on a rank order list is contingent upon submission of a verbal or written statement indicating ranking preferences; or
(c) a program to require applicants to reveal the names or identities of programs to which they have or may apply; or
(d) a program and an applicant in the Matching Program to make any verbal or written contract for appointment to a concurrent year residency or fellowship position prior to the release of the List of Unfilled Programs.
Only the final preferences of programs and applicants, as expressed on their final certified rank order lists, will determine the offering of positions and the placement of applicants through the Matching Program.
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I think the underlined part is key - programs and applicants can say whatever they want about their preferences of their own free will (e.g. you're my #1 vs. you're ranked to match), but neither side can ask the other for their preferences or ask for/expect any commitment based on said preferences.