SAN FRANCISCO (CBS SF) — When San Francisco-Marin Food Bank Director Paul Ash is asked about the impact the new tax law will have on his operation, concern quickly becomes etched across his face.

Ash fears the changes signed into law by President Donald Trump will lead to a decrease in donations.

“We’re really concerned,” he told KPIX 5.

Under the new plan, the standard deduction will double from the current one in 2018. For a single person, it will jump to $12,000 and for a couple to $24,000. So the only people who will be making charitable deductions on their taxes will be those with more than $12,000 or $24,000 in deductions.

“People are in general — better off making a donation this year than they would be next year,” said tax law expert Rob Wood. “Charities understandably worry that they’re going to be adversely impacted, that they’re not going to collect as much money, people are not going to be as generous, that kind of thing.”

According to the Tax Policy Center, charitable giving next year could be slashed by anywhere from $12 billion to $20 billion. For organizations like the food bank, even a small decrease will be a big problem.

“I do believe people give from their heart, but maybe they’re giving 20 percent more because they’re going to get a 20 percent deduction on their tax returns,” Ash said. “And if we have a 20 percent haircut at the food bank, that’s going to be devastating.”