On Wednesday, the Justice Department escalated its fight against 23 so-called sanctuary cities, sending letters asking for greater compliance with federal immigration law.
Landrieu told reporters in Washington that he would not go to the meeting under "false pretenses," complaining that the meeting is supposed to focus on infrastructure but that the Justice Department's sanctuary cities move changed the equation.
"An attack on one of our cities' mayors who is following the Constitution is an attack on all of us. I will not be attending that meeting," he said.
New York City's de Blasio also tweeted that he would not attend.
"I will NOT be attending today's meeting at the White House after @realDonaldTrump's Department of Justice decided to renew their racist assault on our immigrant communities," he wrote. "It doesn't make us safer and it violates America's core values."
A number of mayors did attend, however, and President Donald Trump made brief mention of his Department of Justice's decision and the fact that some mayors had boycotted the event.
"The mayors who chose to boycott this event have put needs of criminal illegal immigrants over law-abiding Americans, but let me tell you, the vast majority of people showed up," Trump said, to applause.
At least the mayors of three cities that received Justice Department letters were meant to attend Wednesday's meeting: Michael Hancock of Denver, Greg Fischer of Louisville, Kentucky, and de Blasio.
In a news conference as the meeting was going on, de Blasio accused Trump of "a slap in the face to our cities and our people."
"This proves there was no intention to have an honest dialogue," de Blasio said, holding the letter. "I came down here expecting a serious meeting, and what I got was a publicity stunt from the Trump administration."
Fischer did attend Wednesday's meeting at the White House, his spokeswoman Jean Porter told CNN, despite his city receiving the letter.
Ahead of the meeting, though, Fischer slammed the Trump administration's decision to send the letter in the first place.
"This notice today is insisting that people send proof that they are in compliance with federal law, and I would bet that many of us up here have already done that," he told reporters in Washington, DC, on Wednesday. "So perhaps the mailbox at DOJ should be checked."
Denver Mayor Michael Hancock decided against going to the White House because of the letter.
"No, won't be going to the WH today, better things to do than be part of a photo op for 45 as he threatens cities again," Hancock tweeted.
At least one Republican mayor decided not to attend the event. A spokesperson for the US Conference of Mayors told CNN that Elizabeth Kautz, the Republican mayor of Burnsville, Minnesota, declined the invite due to the Justice Department. Kautz is a past president of the US Conference of Mayors.
"Our goal here is to ensure compliance with applicable federal law. Our goal is to ensure that jurisdictions that will comply with applicable federal law receive the the grant money and can keep the grant money that they have already obtained," a senior Justice Department official said about the letters.
Cities such as New York have sought to fight Trump's immigration policy, leading the administration to threaten to cut federal funding if they do not comply. Despite their repeated attempts, courts have repeatedly blocked the Justice Department's attempts to crack down on the so-called sanctuary cities.
White House spokeswoman Lindsay Walters said before Landrieu and de Blasio declined to attend that the meeting was meant to focus on "the growing economy, as well as working together to tackle the opioid epidemic and rebuild the nation's aging infrastructure."
After they announced they would decline to attend, Walters said the White House was "disappointed" over their decision to "make a political stunt instead of participating in an important discussion with the President and his administration."
The "working session" between Trump and the mayors was slated to put leaders like Landrieu, de Blasio and Columbia, South Carolina's Stephen Benjamin in the same room with a man whom many of the mayors have used as a rhetorical foil for months, setting up the possibility for contentious exchanges.
Landrieu, whose term in New Orleans ends later this year, has been an outspoken critic of Trump, particularly on the way that he describes cities and his comments about Confederate monuments
. Landrieu is among the Democrats rumored to be eying a presidential run in 2020.
The frequent criticism of Trump from mayors -- including Landrieu -- focuses on the President's efforts to disparage American cities.
"Our cities are a source of American pride," Landrieu, who endorsed Hillary Clinton, wrote in an October 2016 post. "A candidate for President cannot make America prosperous if he doesn't understand that America's cities are, in fact, the backbone of the national economy."
CNN's Tal Kopan and Betsy Klein contributed to this report.