THERE IS A chasm between how MBTA management views the agency’s pension fund and how the union that represents the biggest share of T workers sees the retirement account.

The Fiscal and Management Control Board on Monday spoke with one voice, raising the alarm about a pension system that board members said is worryingly underfunded.

In 2018, investment losses of $50 million and a $224.4 million drawdown of benefits overwhelmed the $123.3 million contributions made to the fund, resulting in negative net cash flow of $151 million in the roughly $1.45 billion fund, according to MBTA officials.

Because of that negative cash flow, on a monthly basis the MBTA Retirement Fund sells some of its liquid investments, according to the T’s chief financial officer, Paul Brandley.

“That’s akin to burning the furniture to heat the house,” said Brian Shortsleeve, a control board member and former general manager of the T. “In a market which is flat-ish, every month this fund’s going to be selling liquid securities to make payments.”

But Boston Carmen’s Union President James O’Brien, himself an MBTA retiree and retirement fund board member, argued the recent market performance was similar to what other pension funds experienced last year, and contended that T management has made the situation appear more dire than it actually is.

“Claims by the MBTA that the Fund is in crisis are simply not true,” O’Brien said in a statement. “The truth is that the MBTA enticed employees into retirement in order to balance the budget and claim a public victory, now they act shocked that those same employees are collecting pensions.”

According to a document prepared by Tom Roth, a lawyer for the union, the combination of contributions from the T and its employees will be enough to meet pension costs through 2039, when the plan will become fully funded, requiring far less in annual contributions.

The disagreement is an old one. Would-be reformers have for years assailed the T retirement fund, casting suspicion on the fund’s management and arguing that it is financially unsound, in part because workers can receive benefits sooner at the T than in other areas of government. The presentation on Monday was made at the request of Shortsleeve, who took on the issue when he was an MBTA executive.

Shortsleeve rejected the idea that the retirement incentives the T offered in recent years to bring its operating costs down were to blame.

“The MBTA pension’s been in free-fall for years. There’s nothing that’s happened in the last three years that accelerated that,” Shortsleeve said after the presentation. “The core issue with the T pension is unsustainable benefit design. It’s a system that incents people to retire early — so more than half your retirees are retiring in [their] fifties.”

Though it receives MBTA funding, the retirement fund is technically private, which presents challenges for those who want to take control of it. Shortsleeve and others favor merging the T retirement fund into the state’s $72 billion pension system.

Other members of the T control board share Shortsleeve’s overall concern with the retirement fund’s performance, including Brian Lang, who is the president of a local union representing hospitality workers, and Joe Aiello, the control board’s chairman.

“I just want to throw out a sense of urgency to all the parties that are at the table,” Aiello told his colleagues. “For the balance sheet of the authority, if we can’t solve for this it eventually deteriorates the amount of service we can put out to the public.”

Brandley warned that the pension fund situation threatens to wipe out the progress made by the control board since it was established in 2015 to reform the finances and operations of the transit system that moves hundreds of thousands in and around Boston every day.

“In the near future this liability has the potential to undo the progress that the board and our management team have made over the past four years towards fiscal sustainability,” Brandley said.

On his way from the public meeting Monday to a closed-door executive session starting right after, Aiello demurred when asked what options the control board or Legislature could take.

“That’s a half-hour discussion. It’s a very complicated matter,” Aiello said.