Mayor Lori Lightfoot has ordered a citywide hiring freeze — including the Chicago Police Department — to chip away at a massive budget shortfall and lay the groundwork for another painful round of tax increases.

The hiring freeze — “across all funds, including grants” — affects 3,000 vacant positions covering roughly 9 percent of the city’s workforce.

The freeze will be a drop in the ocean if the shortfall that former Mayor Rahm Emanuel left behind is, indeed, the $1 billion-plus that Lightfoot claims it is.

But it’s a symbolic and important step as Lightfoot prepares to lower the boom on beleaguered Chicago taxpayers during a Thursday night budget speech.

“With Chicago facing one of the largest budgetary gaps in recent history, these measures are just one part of a broader approach we must take to restore our finances and put Chicago on a path to a stronger, more secure future,” Budget Director Susie Park said in a news release.

The decision to include CPD in the freeze is significant. It will stop a conveyor belt of recruit classes the police academy has churned out since September 2016.

That’s when Emanuel responded to a surge in homicides and other violent crime by launching a two-year plan to add more than 1,000 police officers.

Chicago now has roughly 13,400 sworn officers and dozens of additional sergeants and detectives.

The August class of recruits will apparently be the last for now. The September class has been canceled. October, November and December classes are in limbo, said Park, the Chicago Police Department’s former deputy chief of finance.

“We’re gonna see how, maybe we can hold the hiring freeze for a little bit and maybe have bigger classes towards the end of the year,” Park told the Chicago Sun-Times.

“Right now, they are frozen. ... We are working through, ‘Do we adjust those numbers? What do we need to ensure public safety?’”

Is the hiring freeze a prelude to employee layoffs?

“We are definitely looking at everything, and everything is on the table,” Park said. “We’re looking at every position, all the line-items.”

The Sun-Times has reported Lightfoot plans to ask the Democrat-controlled General Assembly to let the city tax high-end professional services and raise the transfer tax on big-ticket home sales.

Park said it was “too soon to say” whether a property tax increase could be avoided if the mayor gets what she wants from Springfield.

In her memo to department heads, Park stressed exceptions to the hiring freeze will be allowed only if job offers have been made, interviews have been scheduled or the hirings include filling “priority positions that directly affect the health and safety” of Chicago residents.

The out-clause will make certain that police, fire and aviation “remain staffed and prepared for seasonal work,” Park said.

“Our goal is to try to keep up with [police] attrition. We’re no longer doing 100-recruit classes a month anymore. The goal is to sustain that two-year hiring surge,” she said.

Noting 200 detectives have been hired to improve the police department’s dismal homicide clearance rate, Park said, “Part of that discussion with CPD is to make sure, in that rank, that we are keeping up.”

Before leaving for vacation, the mayor told reporters she plans to put a heavy emphasis on cost-cutting to convince taxpayers who have already paid a $2 billion price to help Emanuel chip away at the city’s pension crisis that “we understand the pain and the burden they have been facing with taxes.”

“I get it. I hear it everywhere I go — particularly around property taxes. And I’m very mindful of that,” Lightfoot said.

“But the reality is — given the gap that we’re gonna face next year, given the pension payments that are demanded — we are gonna have to look for additional revenue sources. There’s no question about that.”