Senator Kirsten Gillibrand plans to use a prerogative given to home-state senators to try to block the confirmation of Geoffrey S. Berman if he is nominated by President Trump as the United States attorney in Manhattan, her spokesman said on Wednesday.

The senator, Democrat of New York, intends to use her “blue-slip prerogative” to lodge her objection over reports that President Trump had personally interviewed Mr. Berman as part of the selection process.

Ms. Gillibrand, through her spokesman, said those reports were deeply disturbing, because of conflicts of interest inherent in Mr. Berman’s “potential jurisdiction on matters that could affect the president personally.”

“Under these circumstances,” Ms. Gillibrand’s spokesman, Glen Caplin, said, if such a meeting took place and Mr. Berman were nominated as United States attorney, “the senator would have no choice but to stand up for the independence of this office by using her blue-slip prerogative.”