The service cuts are the latest setback for the MBTA, which has struggled to run the subway system safely and effectively despite years of public pressure to improve, extra funding for capital projects, and low ridership levels during the pandemic.

They are also a direct response to orders from the Federal Transit Administration, which has been investigating T operations since a series of accidents, including the death of one rider, occurred over a short time period recently. On Wednesday the FTA issued a grim assessment of safety at the T, citing staffing shortages and describing subway dispatchers working 20-hour shifts in the Operations Control Center. As of April 29, four out of 18 heavy rail dispatcher positions and two out of 11 supervisor jobs were vacant, the FTA found.

“With a limited number of dispatchers, these new timetables allow the MBTA to schedule dispatchers in compliance with Federal Transit Administration directives, and continue delivering service in a safe and reliable manner,” the T said in a statement.

On Friday, transit advocates and business leaders said they’ve warned the MBTA for years it had to do a better job prioritizing safety and investing in its workforce, or face service reductions that will strain the economy and disproportionately hit low-income residents.

Longer wait times between trains, they said, will be felt most deeply among T riders who can’t work from home and lack other transportation options. Fewer trains, they said, will also delay the MBTA’s efforts to restore ridership to pre-pandemic levels.

“I am so frustrated,” Boston Mayor Michelle Wu said Friday at an unrelated event. The T should have never let conditions deteriorate, she said, to the point where federal intervention was required.

“In a moment when public transportation is more important than ever, we have to stop and take care of issues that should have been resolved long ago,” Wu said.

James E. Rooney, chief executive of the Greater Boston Chamber of Commerce, and a former T official, called the service reduction “unacceptable.”

“The MBTA announcement of service cuts is yet again another set back from the T that demands our residents unfairly scramble to figure out alternative plans to commute to work and downtown,” he said in a statement. “Our residents and families deserve a strong transportation system that is reliable and safe.”

The FTA, in its directive, gave the MBTA 48 hours to submit a detailed staffing plan for subway dispatchers that ensures the workers get enough rest between shifts. The plan must be in effect for at least six weeks and the MBTA has to prove it is giving subway dispatchers appropriate time for rest, according to the directive. On Friday, an FTA spokeswoman said the agency had no comment.

“It’s a double whammy,” said Rick Dimino, chief executive of A Better City, a group of business leaders that lobbies for transportation and other improvements. “There are questions about T safety and now there are going to be questions about the T’s reliability.”

The MBTA said the new weekday schedules on the three lines will remain in effect for the rest of the summer. The agency said it is exploring options for adding more staff to the Operations Control Center, including a recruitment campaign, $10,000 hiring bonuses for heavy rail dispatchers, and the possibility of returning former dispatchers to work.

T ridership remains well below pre-pandemic levels. As of last week, ridership on the Red and Orange lines remained approximately 50 percent below pre-pandemic levels while Blue Line volume was about 44 percent below, the MBTA said.

Dimino questioned whether the MBTA had considered hiring outside contractors or moving managers into the dispatch center temporarily before it decided to cut weekday service.

“It’s turning their backs on their ridership,” he said. “This is not a time when transit service cutbacks should be happening.”

State Representative William Straus, House chairman of the Joint Committee on Transportation, said the MBTA budget has the money to pay for short-term staffing.

“The T has the finances to address this now,” he said.

Governor Charlie Baker’s office didn’t respond Friday to a request for comment.

In its directives, the FTA said the MBTA’s investments in capital projects dwarf those for day-to-day maintenance of its older equipment, limiting critical upkeep.

Transit advocates seized on the FTA’s observation and criticized the MBTA for reallocating $500 million in operating funds earlier this year to pay for capital improvements.

Stacy Thompson, executive director at LivableStreets Alliance, said the T has to offer prospective employees better pay, benefits, and working conditions to compete with private sector employers.

“For those who have been paying attention, we’ve seen this coming for a long time. We’ve been screaming into the void that you must invest to operations in order for the system to run,” she said.

Under the new schedule, the longest waits will be on the southern end of the Red Line along the Ashmont and Braintree branches, when weekday trains will operate every 14 to 15 minutes, the T said. Red Line trains running between Alewife and JFK/UMass stations will run every seven to eight minutes.

The normal summer schedule for the Red Line is typically nine to 10 minutes between trains during rush-hour periods, 10 to 12 minutes during off-peak hours, and every five to six minutes on the section between Alewife and JFK/UMass stations, the T said.

On the Orange Line, weekday trains will operate every 10 minutes in the mornings, with 11 minutes between trains during the evening, and eight to nine minutes during mid-day periods. Those are as much as four minutes slower than normal scheduling, depending on the time of day.

On the Blue Line, weekday trains will operate every seven minutes until 9 a.m., and every eight to nine minutes for the rest of the day, about one to two minutes slower for most of the day.

Emma Platoff of the Globe staff contributed to this report.