TORONTO -- Ontario's education ministry is recommending school boards freeze hiring as the government consults on class sizes and hiring practices.

Deputy minister Nancy Naylor sent boards a memo Thursday noting that the government implemented a hiring freeze in June and that school boards may wish to institute similar measures.

When that public service hiring freeze was instituted, the government said it didn't apply to front-line staff such as police and fire services, and Premier Doug Ford said it also didn't apply to nurses or teachers.

Naylor advised the boards this week to defer filling vacancies for retirements and other leaves for teachers and other staff until the minister gives them an update by March 15.

"I am writing to you today to recommend that school boards exercise prudence in making hiring decisions in light of the upcoming Ontario budget and the recent consultation on class size and hiring practices," she wrote in the memo.

The consultations launched in January contemplate the possibility of removing class size caps for kindergarten and primary grades.

NDP education critic Marit Stiles suggested the promise of an "update" by March 15 is ominous.

"The Conservatives, I believe, have just put families on notice that deep cuts are coming to their children's education," she said.

Education Minister Lisa Thompson's office did not make her available for an interview, but she said in a statement that her priority is ensuring all students have access to a meaningful education.

"To achieve this, we need to take a hard look at how school boards spend their money and make sure every single dollar invested in our education system is a dollar invested in a student's future," Thompson wrote.