Metro workers gathered Sunday at the ATU Local 689 union hall in Forestville, Md., to authorize a possible strike. (ATU Local 689)

Tension between Metro and its unionized workers is at its highest level in four decades, both sides say — the culmination of management’s aggressive push to instill a safety culture and hold down costs as the union battles to protect workers.

The union’s decision Sunday to authorize a strike capped two years of escalating animosity between Metro General Manager Paul J. Wiedefeld and the agency’s workforce, and it threatened to lure the system’s hundreds of thousands of daily commuters into the dispute.

Metro Board Chairman Jack Evans said the agency is taking the union’s strike vote seriously and does not view it as an “empty threat.”

“I think it’s a real, legitimate concern,” he said.

On Monday evening, the union announced that its leadership would meet with Metro on Tuesday. “It is not our intention to disrupt the MLB All-Star game,” the union said in a statement, downplaying suggestions that a strike was imminent. Major League Baseball is holding All-Star Game events at Nationals Park this week, culminating in the nationally televised game Tuesday.

“We would hope that WMATA shares our desire to talk in good faith and will not use this meeting as a stop gap to get through the big day,” the statement said.

The union did not address questions Monday about whether it planned to walk out after the All-Star Game. But 94 percent of participating members voted Sunday night to give union leadership the authority to order a work stoppage. (The union, which represents about 8,000 of Metro’s 12,500 employees, declined to specify how many members voted but said it was in the thousands.)

The tension heightened recently just as the agency for the first time obtained dedicated funding from Maryland, Virginia and the District, the three jurisdictions it serves.

But the $500 million in annual funding is contingent upon keeping costs down, and Wiedefeld has sought to control the agency’s labor spending as new caps on operating costs approach. In addition, the union and Metro could not find common ground on contract matters such as retirement plans and health benefits, forcing the contract to binding arbitration. A ruling is expected soon.

“Their concerns are noted and I take them seriously, but they are not something that is easily resolvable given Metro’s financial situation,” Evans said. “The arbitrator should decide [on the contract.] Other than that, there’s not an action that I think Metro could take that would assuage the concerns of the labor union at this point in time.”

Metro said Monday that Wiedefeld has adopted a strategy aimed at improving service and instilling better efficiency. But the union issued a statement later in the day calling the agency’s statement as “tone deaf as it is willfully ignorant.”

Striking is illegal under the federal and regional Metro compact, which requires collective bargaining to resolve disputes and binding arbitration if talks fall through. That doesn’t mean the union won’t strike. It did so for a week in 1978 over Metro’s failure to provide a contractually obligated 20-cent-an-hour cost-of-living increase.

But striking would be a risky prospect for the labor group, legal experts said.

Manesh K. Rath, an attorney and expert in transportation law, said Metro could seek to immediately end a strike in federal court, because such an action is illegal under the compact.

“A federal court could hold that the strike is indeed illegal and order workers to return to their jobs immediately,” he said. If they don’t, the workers could be held in contempt of court, and the court could levy steep fines against the union. In a particularly dramatic example of a similar case, striking New York City transit workers were fined $1 million per day in 2005.

Relations between the union and Wiedefeld have not always been so tense. When Wiedefeld first started Metro’s top job in fall 2015, union president Jackie Jeter said she was optimistic that new leadership would mean good things for workers — more honesty from management, stricter adherence to safety protocol, an acknowledgment that many of the transit agency’s problems and shortcomings were rooted in the ranks of supervisors.

But opposition from the union to Wiedefeld’s leadership has grown. Chanting, protests, signs and disruption have become a regular occurrence at the Metro board’s monthly meetings. Threats of labor action have become increasingly frequent in response to changes to sick leave, stagnant wages and threats of privatization.

Just last month, the workers who packed the seats in the Metro boardroom erupted in chants after a union leader shared photos of putrid conditions in bathrooms at bus depots and rail yards — facilities that they say have become increasingly dirty after janitorial duties were outsourced to a private company.

When lawmakers began discussing legislation that would provide steady funding to the ailing transit system, many officials said they wanted to diminish the power of Metro’s union, make it easier for management to fire workers and place limitations on workers’ ability to receive overtime.

Ultimately, those kinds of specific strictures were not included in the legislation passed by the District, Maryland and Virginia. Instead, Virginia and Maryland enacted a broader measure aimed at holding down labor costs and other expenses by requiring Metro to limit its annual increases in operating subsidies to 3 percent.

On Monday, the Republican leaders of the Virginia House of Delegates said they still have concerns about the commitment of Metro’s largest union to help improve the transit system.

“The ATU’s action threatens not only to cripple the region, but also to do significant damage to the political progress we’ve made over the last year,” House Speaker Kirk Cox, Majority Leader Todd Gilbert, Caucus Chairman Tim Hugo and Majority Whip Nick Rush said in a statement. “We will not write a blank check to a dysfunctional organization.”

Those lawmakers urged Virginia Gov. Ralph Northam (D) and Attorney General Mark Herring (D) to take legal action against the union, and seek a federal court order to bar the union from pursuing a strike.

With Tuesday’s All-Star Game looming, and a six-week Red Line segment shutdown beginning this weekend, some saw a disaster in the making. Metro observers drew parallels to the day-long Metro shutdown in March 2016, when Wiedefeld ordered the rail system closed for emergency cable inspections.

“The problem is, this is like the safety shutdown on steroids,” said Kevin Heaslip, associate civil and engineering professor at Virginia Tech, who specializes in public transportation. “This is the buses, this is the paratransit, this is the whole system. . . . If it happens in the next day or so [you have] the embarrassment of it happening during a large event like the All-Star Game.”