New York Laws
Title 11 - Consideration; Effect of Writing on Requirement of Consideration
5-1111 - Execution by Agent in Real Property Transactions; Written Authorization Required.

ยง 5-1111. Execution by agent in real property transactions; written
authorization required. If executed by an agent, any agreement,
promise, undertaking, assignment or offer required by section 5-1103,
5-1105, 5-1107 or 5-1109 to be in writing, which affects or relates to
real property or an interest therein in any manner stated in
subdivisions one or two of section 5-703 of this chapter, shall be void
unless such agent was thereunto authorized in writing.