NEW YORK - New York City will require all municipal workers to either receive the COVID-19 vaccine before the reopening of schools in September or get tested weekly for the coronavirus, Mayor Bill de Blasio announced Monday.

The decision comes as the daily number of new COVID-19 cases continues to rise, and as the delta variant spreads infections through unvaccinated areas of the city. On Monday, the number of newly reported infections was 837, the highest in more than two months.

Last week, de Blasio announced a similar testing mandate for city health workers as he made the case for both public and private employers to adopt more stringent vaccination requirements. 

"Our goal here is simple: make it maximally easy for people to get vaccinated, and create an atmosphere where there's consequences if you don't get vaccinated," de Blasio said at a news conference. 

The city will also toughen its monitoring of mask-wearing in city offices, de Blasio said, and unvaccinated workers who refuse to wear a mask at their work station will be asked to either immediately go get vaccinated or leave work without pay. 

"We're just not gonna tolerate unvaccinated city employees doing the wrong thing," he said. 

The new mandate will apply to about 340,000 city workers, including teachers and police officers. The mandate is set to begin Sept. 13, when children return to city public schools.

"In September, everything's going to come together," de Blasio said. "September is the pivot point of the recovery."

Health workers in clinical settings will face vaccination or weekly testing starting Aug. 2, while city employees who work in congregate or residential settings have until Aug. 16.

De Blasio framed the new mandate in part as a signal to private employers, who he encouraged to issue similar mandates and to make use of a new app the city has developed to allow employees to show proof of either vaccination or a new COVID-19 test each week. 

"My message to the private sector is, go as far as you can go right now," he said. "I would strongly urge a vaccination mandate whenever possible."

Dr. Dave Chokshi, the city health commissioner, said that the rate of public employee vaccination tracks with the overall city population's vaccination rate. About 71% of adults have received at least one dose of the vaccine, according to city data.

Some city agencies, such as the NYPD, have reported substantially lower vaccination rates than that. However, the agencies say they only have data for the employees vaccinated by the city, and not for those who were vaccinated by their doctors or by private vaccine providers.

De Blasio indicated that he decided on the testing-or-vaccination mandate without direct consultation with unions, but said that the city was currently in conversations with unions about it, and that the city was on firm legal ground in issuing the ultimatum.

"When it comes to the health and safety of our workers in the middle of a global pandemic, we have the right as employers to take urgent action to protect our workers, to protect their lives," de Blasio said. 

The United Federation of Teachers, which represents city workers in schools, indicated it was on board with the the mandate. However, DC37, the city's largest public employee union, pushed back on the unilateral decision to implement the mandate. 

"If City Hall intends to test our members weekly, they must first meet us at the table to bargain," DC37 executive director Henry Garrido said in an emailed statement. 

The unions for both police detectives and firefighters signaled their strong opposition to the proposed rule. 

"This is not about politics, but about the personal rights of our members not to be forced in any way into making a decision based on a risk of punishment by the City," Paul DiGiacomo, the president of the Detectives' Endowment Association, said in a statement. 

Fire department union officials said at a Monday afternoon news conference that they were "pro-vaccine, but we're also pro-choice." Half the union's members are fully vaccinated, according to Andrew Ansbro, the president of the Uniformed Firefighters Association.

"Personally, I don't agree with a member's decision to not get vaccinated, but it is a decision I'll protect," Ansbro said. 

A spokesperson for de Blasio did not respond to emailed questions about whether city workers would get time off to deal with potential side effects from the vaccine or whether the city will require workers who choose the testing option to get tested on their own time.

De Blasio said that he would consider additional vaccine rules for the city if new cases continue to rise, leaving behind his earlier attitude of leaning on city messaging and grassroots organizing efforts to encourage vaccination. 

"The purely voluntary phase is ending," he said. "It's now time to add additional tools."