The Chicago Teachers Union is calling for a tougher approach to combating the coronavirus delta variant ahead of the new school year, suggesting that in-person instruction could be once again paused if cases continue to climb. 

In a Wednesday letter addressed to Mayor Lori Lightfoot, Chicago Public School officials, and members of the school board, CTU said "new pandemic variants pose immediate threats to the health of all Chicagoans, but especially our unvaccinated student population." 

FILE: Pre-kindergarten teacher Sarah McCarthy works with a student at Dawes Elementary in Chicago. 

FILE: Pre-kindergarten teacher Sarah McCarthy works with a student at Dawes Elementary in Chicago.  ((Ashlee Rezin Garcia/Chicago Sun-Times via AP, Pool, File))

CTU applauded Illinois Democratic Gov. J.B. Pritzker’s recent mask mandate for students returning to schools this fall, regardless of vaccination status, but said its "school communities need more than masking to ensure safety – especially as we continue to learn about the delta variant." 

CTU listed recommendations for ensuring safety. Among these was the maintenance of criteria and health metrics based on the prevalence of COVID "to pause in-person instruction." 

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As of now, CPS students are scheduled to return to classes on August 30. 

CPS elementary and middle school students returned to part-time in-person instruction in February, while high school students returned in April, after a year of distance learning due to the COVID-19 pandemic. 

Like many major school districts nationwide, negotiations over CPS students returning to in-person learning proved tedious as the school district and union bumped heads over the idea. 

The possibility of once again pausing in-person instruction comes amid a nationwide uptick in the more contagious variant of COVID-19. 

Last week, American Federation of Teachers (AFT) President Randi Weingarten got pushback after suggesting that school reopenings this fall are not a done deal. 

"So the bottom line is, we're going to keep kids safe, we're going to keep our members safe, we're going to try to open up schools, and we're going to move through this political battlefield," Weingarten said.

Critics picked up on her comment about the reopening of schools because it sounded like backpedaling from when she argued in May that "we can and we must reopen schools in the fall." 

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Fox News has reached out to CTU and CPS with a request for comment and will update this story accordingly. 

Fox News' Cortney O'Brien contributed to this report.