Faced with a report that the MBTA’s pension fund will need about $1 billion over the next 18 years to remain solvent and fulfill its obligations, the T’s Fiscal and Management Control Board on Monday was presented with three options: negotiate changes to pension agreement terms through the collective bargaining process with its largest union, pursue arbitration or ask the Legislature to step in.

As MBTA pension assets have declined by 23 percent in the last decade, the contribution from the T has increased 135 percent from $37 million in fiscal year 2007 to $87 million in the current budget, according to the T.

Without action, the funded level is expected to fall below 50 percent within five years, according to the T report, and the fund would need $3 billion in funding to meet its obligations through 2035.

Part of the problem is that since 2010 the T has had more retirees drawing from the pension fund than employees paying into it. According to the report, there are currently 899 more retirees drawing money from the pension than there are employees paying into it.

The fund got a 6.2 percent return on its investments in 2016, according to preliminary figures, a 0.7 percent return in 2015, and a 4.8 percent return in 2014 – each falling short of the fund’s 7.75 percent target return. In 2012 and 2013, respectively, the fund saw returns of 14 percent and 16.4 percent.

The state pension fund managed by PRIM reported a 7.6 percent return in 2016, compared to the T pension fund’s 6.2 percent return. Gov. Charlie Baker has previously recommended the MBTA Retirement Fund be merged into the account managed by PRIM, and his fiscal 2018 budget proposal included an outside section allowing such a merger. The House and Senate have both included the provision in their own budget proposals as well.