As Metro struggles to respond to federal safety mandates, keep up with systemwide repairs and overhaul its entire track inspection department, it has dramatically increased its reliance on private contractors to perform core functions for which it lacks qualified workers.

It’s a trend that concerns union officials and employees who say they fear the move is part of a push toward privatization.

The operations funding the agency has spent on private contractors has nearly doubled in the past two years, from $24.8 million in fiscal 2015 to $47.4 million in fiscal 2017, according to financial documents.

General Manager Paul J. Wiedefeld’s proposed fiscal 2018 operating budget ups that amount to nearly $65 million. .

Some of that money is dedicated to relatively peripheral needs, such as maintenance costs at newly opened Metro facilities. Other outsourced tasks are inherently temporary: consultants hired to vet and rewrite Metro’s track inspection manual, or safety experts brought in to help the agency fulfill the dozens of recommendations made by the National Transportation Safety Board and the Federal Transit Administration.

But in other cases, the distinction between the jobs performed by private contractors and longtime Metro staff members has become more blurred. Union leaders say the increased dependence on outside labor is especially galling in light of Wiedefeld’s plans to eliminate 500 staff positions in fiscal 2018 in addition to 500 job cuts he announced this past spring.

Union representatives also argue that contract workers lack familiarity with Metro’s particular issues, are prone to performing substandard work and allow the transit agency to avoid paying for better training for its own workers.

“Private contractors working on SafeTrack . . . outnumber us almost 2 to 1,” said Tony Gough, a track maintenance worker who spoke at a Metro board meeting in October. “But who from [the Washington Metropolitan Area Transit Authority] oversees contractor work to ensure that the work is not just getting done, but getting done correctly? . . . There have been too many times that employees have had to redo work that has been done by private contractors.”

Metro spokesman Richard L. Jordan said that the exact percentage of SafeTrack work performed by contract labor is “difficult to assess” but that officials think it is “about half.”

“In general, Metro fully utilizes the Local 689 [union] crews and then supplements with contractors to maximize the amount of work that can be performed while the track is out of service,” Jordan said.

[Metro workers: Management forces us to put service before safety]

Asked about the union’s concerns last week, Wiedefeld pointed out that many of the jobs performed by contractors are temporary positions intended to help the transit agency respond to federal safety recommendations. But, he acknowledged, “we do look at opportunities to bring in other resources.”

“We have a contract, so we have to live by that,” Wiedefeld said. “But when there are opportunities to do other things that maybe provide a better product, or are more efficient — or there are new things that we want to take on — we’re not closing those options, either.”

Jackie L. Jeter, president of the Amalgamated Transit Union Local 689, said the union has asked Metro for information on the number of outside contractors employed to perform core jobs such as track inspection and maintenance. So far, she said, the union has received no response.

The issue of the purview and limits of private contractors’ work has gained increased attention in recent weeks after Wiedefeld fired 21 track inspectors and supervisors for allegedly falsifying inspection records; 14 other workers were disciplined.

For its long-term needs, Metro is hiring and training new staff for its inspection department and retraining the remaining employees. But Wiedefeld also hired 10 contract inspectors to fill out the department in the short term.

[One-third of Metro’s track inspection department has been fired for falsifying records, Wiedefeld confirms]

Jeter said she is particularly concerned about the agency’s decision to begin hiring contract inspectors before it had notified those on its staff that they were being fired.

“We’re trying to find out exactly when did this hiring start, and what are their roles, and what are the jobs that they’re doing,” Jeter said. “There are a lot of contractors on the property, and we need to find out exactly where they are and what they’re supposed to be doing.”

Metro has already made formal moves toward permanently privatizing some of its major responsibilities. Last year, the agency put out a request for proposals for a company to manage parking services. The agency also plans to pilot a program that would allow ride-hailing companies such as Uber and Lyft to provide some paratransit services to people with limited mobility.

[Metro plan to privatize parking could result in fee hikes]

Even so, board member Michael Goldman, chairman of the board’s finance committee, acknowledged that privatization isn’t a long-term answer to the agency’s problems. When it comes to tasks such as track inspections, rail repairs and safety improvements, reliance on outside help is a temporary measure made necessary by the dramatic steps that must be taken for Metro to right itself, he said.

In the long term, he said, he wants to see privatization limited to jobs that are not central to Metro’s rail and bus operations.

“I think these things absolutely should be internal, and they should be WMATA employees. We shouldn’t be relying on outside contractors to do these functions as part of the normal business of operating a transit system,” Goldman said. “On the essential safety functions, those are things we should be getting back to relying on WMATA employees to perform.”

Still, the increased spending on contract labor is part of a larger national trend, as transit agencies around the country seek to cut costs by privatizing work than can be done more cheaply by outside contractors.

And, in some cases, just the threat of privatization has monetary value. At the Massachusetts Bay Transportation Authority, Boston’s transit system, state officials celebrated the conclusion of contract negotiations in December after they won a slew of concessions from the area’s transit unions. By the end of the process, the unions had agreed to defer a scheduled wage increase, lower the wage rate for new employees and limit workers’ ability to collect overtime pay. The state expects to save $81 million over the next four years.

How? According to Massachusetts Transportation Secretary Stephanie Pollack, the state was able to push back against the transit unions by taking serious steps toward privatizing central roles at the MBTA. Officials sought out proposals from private companies about how much they would charge to take on basic services.

Then, the state delivered an ultimatum to the transit unions: Beat that price, or we’ll skip binding arbitration and simply contract out those jobs.

“When we talked about privatization, we didn’t put it on the table as a threat — we put it on the table as a tool,” Pollack said. “And when they realized that we were serious . . . it changed the dynamic at the negotiating table in a substantial way.”