Sen. Kirsten Gillibrand’s office smacked down Mayor Bill de Blasio when hizzoner asked if he could attend Tuesday’s press conference to celebrate the passage of the 9/11 Victim Compensation Fund bill, The Post has learned.

Gillibrand is the chief author of the bill and she and de Blasio are duking it out as bottom-tier candidates in the Democratic primary for president — both polling at or below 1%.

De Blasio held three campaign events in DC Tuesday.

De Blasio spokeswoman Freddi Goldstein confirmed that the mayor’s office had asked Gillibrand’s staff to attend the event — but was told no.

“We asked to participate and were told the event was about the first responders and attendance was limited to sponsors of the bill and advocates,” Goldstein said.

“We would have been honored to attend but recognize that today is about something much bigger than us.”

The mayor even offered not to speak.

The Tuesday afternoon press conference with lawmakers, first responders and former “The Daily Show” host Jon Stewart attending, took place directly after the Senate passed the 9/11 bill, which gives payouts to first responders and other victims of toxic contamination spewing from Ground Zero after the terror attacks.

Sources said said it’s no coincidence de Blasio and Gillibrand are competing against each other in the presidential race.

“Twice he asked to attend and was told no. Two New Yorkers running for president. Read between the lines,” one source familiar with the request said.

Gillibrand’s office did not dispute it blocked the mayor from attending.

An aide to the senator said the event was designed to be focused not on politics but on the first responders, family members and advocates who have been at the Capitol time and time again seeking relief.

“The spirit of the event was to give this group of men and women who have been fighting together for 15 years a moment to speak together as a group and to put the focus on them,” the aide said.

The elected officials invited to the press conference were the bill’s sponsors, the aide added.

While in DC, de Blasio officially announced his Workers’ Bill of Rights at the headquarters of the Communications Workers of America. He then headed to the Muslim Collective for Equitable Democracy Conference.

Later, he added a stop at a rally at Ronald Reagan Washington National Airport to join airline catering workers’ push for $15 in minimum pay.

Additional reporting by Marisa Schultz