The onslaught of toll increases at the Golden Gate Bridge is not likely to subside as span authorities face looming budget deficits.

A five-year toll plan initiated in 2014 has raised $138 million and has helped the agency stay in the black. The price to cross the bridge will tick up by 25 cents July 1 — bringing the toll to $8 for some drivers — as part of that plan.

But after that hike, no more toll increases are scheduled. The bridge board will need to decide if more toll hikes are needed, a discussion that will happen this fall.

All indicators are more toll increases will be needed. On Thursday, officials reported a $3.9 million deficit for the coming fiscal year. That hole can be filled by reserves. But the latest financial forecasts from the district also show a $72 million five-year deficit and a $360 million 10-year deficit. The deficits are primarily due to increases in salaries, medical coverage, pension costs and depreciation.

Tolls are the principal source of funding for the agency.

“It does raise the issue about what are we going to do moving forward,” said Denis Mulligan, general manager of the bridge district. “When the board meets in the fall they will talk about all options. One of the options is do we want to have a conversation with the public about tolls. The board will have to make policy choices … If you look further out, our financial future looks cloudy. Costs seem to go up every year. If revenue remains flat, it will put pressure on the service we provide.”

At the present $7.75 toll for those without FasTrak, the Golden Gate Bridge by far has the highest toll in the Bay Area. All other bridges charge $5, except the Bay Bridge, which goes as high as $6 during peak commute periods. The Golden Gate Bridge is managed by a special district with its own board, while the rest of the region’s toll spans are operated by Caltrans.

Marin residents bear the brunt of Golden Gate tolls. County drivers make up almost 40 percent of those who cross the span, according to the most recent license plate data from the bridge district. San Francisco residents make up 23 percent of crossings, Sonoma residents about 11 percent.

“We are quite concerned that the cost of commuting will become prohibitive for the average worker,” said Mimi Willard of Kentfield, founder and president of the Coalition of Sensible Taxpayers.

Bridge officials have noted that Marin enjoys the majority of toll-subsidized transit — bus and ferry service — which they say has cut traffic on Highway 101 by as much as 25 percent during peak commute hours.

With all-electronic tolls now on the bridge — toll takers were eliminated in March 2013 — the cost to cross can increase by less than whole-dollar increments without fear of a traffic backup, because no change has to be made. After an initial $1 toll boost in 2014, the fee has increased by 25 cents each year since and in July will jump to $7 for FasTrak users and $8 for pay-by-plate drivers.

Carpools — vehicles with three or more people from 5 to 9 a.m. and 4 to 6 p.m. — now pay $4.75 and will see the fee go to $5.

Kate Sears, a bridge board member and Marin County supervisor, said the toll issue will not be taken lightly.

“We all want to have a heightened sensitivity about any increase,” she said. “You know what our world is like now. Housing is impossible and everything is more expensive. That means we need to be much more focused than in the past when considering whether it makes sense to increase tolls. Every little increase is hard, especially for our young people and seniors.”