Shaina Newman will lose her Starbucks money if Congress decreases an employer-sponsored federal tax-advantaged transit benefit this month.

“It will cost me an extra $60 a month,” said Newman, 26, who rides the Newburyport/Rockport commuter rail line daily. “I’d just have to tighten my budget and not be able to buy coffee.”

The nearly 50 percent reduction — from $230 a month to $120 per month — could affect 129,000 commuter rail riders who buy pre-tax commuter rail passes through their employers.

“The average person taking the commuter rail from Zone 5 or out won’t be able to pay for their entire trip with pre-tax funds,” said Jeremy Doak of the Transportation Benefits Association, who commutes from Attleboro to Watertown.

“I only pay for $50 with post-tax funds. It’s a significant drop in what I’m able to spend on my commute.”

Part of the 2009 bailout package, the benefit has a 50 percent chance of being extended, according to Doak.

Brian Kane of the MBTA Advisory Board isn’t so optimistic.

“This will drive down ridership,” he said. “The T can’t afford this right now. This is a disaster across the board. I really hope our legislators will, frankly, do something about this.”

Kane and Doak are dumbfounded that similar parking benefits for drivers aren’t on the chopping block.