The Massachusetts Bay Transportation Authority, after hundreds of employees took buyouts and amid major vacancies in top positions, may still lay off workers, officials said, as the agency faces a potential $110 million deficit.

A recent downturn in sales tax collections could bring in about $32 million less than expected in state funding for the agency, said Brian Shortsleeve, the MBTA’s acting general manager at Monday’s weekly fiscal control board meeting.

“Everything’s on the table,’’ he said. “We’re going department by department, identifying areas where we can streamline and run more efficiently.’’

Any layoffs would come after more than 260 departing employees took buyouts — about $13.3 million in annual savings. Shortsleeve said the agency will hire replacements for 110 of the workers who took advantage of the buyouts earlier this year.

But then nearly 150 additional positions will have to be eliminated to reach the agency’s goal of cutting 300 positions off the payroll, according to Shortsleeve. The agency is continuing to pursue privatizing various departments, and officials have said they are still reviewing an “involuntary’’ separation program.

In addition to the buyouts, the agency has left vacant about 18 percent of its top jobs, including half of the top staff in the maintenance department, and a human resources director who would help recruit and hire for such positions.

Yet even amid the threats of privatization and layoffs, T officials said the agency is still hiring many people, and more quickly than usual. Nearly 500 employees were hired during this calendar year, and about 767 employees were hired in 2015, according to Jessie Saintcyr, the assistant secretary of human resources for the T and state Transportation Department.

She said the T is still trying to modernize its human resources department. The agency uses a software system that is 10 years old, and about two versions behind the industry standard, Saintcyr said.

Also during Monday’s meeting, board members approved a $10 million contract to Jacobs Engineering for the program management of its project to install “positive train control,’’ a form of anticollision technology, on the MBTA’s commuter rail.

The technology, which is required by federal law, will cost the MBTA about $459 million, according to Bradley Kesler, the chief railroad officer for the T. The MBTA hopes to finish the installation by 2020, which would put it among the last public agencies running a railroad to get the technology.

Officials announced the proposal to install the technology in November without a public plan to fund it. In the T’s current finance plan, about 67 percent will come from federal loans, another 13 percent will come from federal grants, and the MBTA will have to chip in about 20 percent — or $93 million — of its own cash.

The major project will also send additional funds to Keolis Commuter Services, the money-losing operator of the agency’s commuter rail. According to a budget presented Monday, Keolis could be paid about $25 million to oversee the work of the contractors and help install the technology.

In addition, Boston Carmen’s Union president James O’Brien on Monday criticized the T, saying that a dozen MBTA fare-collecting machines were recently left too full of money to work after T management changed the routes of the employees who drive across the region to collect cash fares.

“We received notices from employees that fare gates were being left open to accommodate the amount of riders who had to be given free trips due to inoperable fare machines,’’ he said.

But T officials on Monday pushed back on the assertion, saying that full fare machines are not uncommon, and that the T needed to consolidate the routes.

Nicholas Easley, the T’s director of flexible contracting, said there are more than 300 “full-service vending machines’’ and “every day, some of those fill up.’’

Nicole Dungca can be reached at nicole.dungca@globe.com. Follow her on Twitter @ndungca.