Alexander Acosta, the US labor secretary under fire for having granted Jeffrey Epstein immunity from federal prosecution in 2008, after the billionaire was investigated for having run a child sex trafficking ring, is proposing 80% funding cuts for the government agency that combats child sex trafficking.

Acosta’s plan to slash funding of a critical federal agency in the fight against the sexual exploitation of children is contained in his financial plans for the Department of Labor for fiscal year 2020. In it, he proposes decimating the resources of a section of his own department known as the International Labor Affairs Bureau (ILAB).

The bureau’s budget would fall from $68m last year to just $18.5m. The proposed reduction is so drastic that experts say it would effectively kill off many federal efforts to curb sex trafficking and put the lives of large numbers of children at risk.

ILAB has the task of countering human trafficking, child labor and forced labor across the US and around the world. Its mission is “to promote a fair global playing field for workers” and it is seen as a crucial leader in efforts to crack down on the sex trafficking of minors.

Katherine Clark, a congresswoman from Massachusetts, said Acosta’s proposed cut was “reckless” and “amoral”. When seen alongside the sweetheart plea deal he granted Epstein in 2008, when Acosta was the US attorney in Miami, she said, it indicated that the labor secretary did not see protecting vulnerable children as a priority.

“This is now a pattern,” Clark told the Guardian. “Like so many in this administration Mr Acosta chooses the powerful and wealthy over the vulnerable and victims of sexual assault and it is time that he finds another line of work.”

Clark grilled Acosta about the proposed cuts in April, when he presented his departmental budget to the House appropriations subcommittee. On that occasion, she said, she found him “rude, dismissive, challenging”.

“I’m sure this is a very uncomfortable topic for him,” Clark said, “but I don’t think he should be able to hide from it.”

Acosta is facing mounting pressure from Democrats to resign, over the lenient deal he gave Epstein and in the wake of the billionaire’s new prosecution. Epstein was arrested on Saturday and indicted on two sex trafficking counts by federal prosecutors in the southern district of New York in an apparent rebuke to Acosta’s earlier decision.

Under the 2008 deal negotiated by Acosta, an FBI investigation that had produced a 53-page draft indictment involving more than 30 potential underage victims was shut down. The billionaire only had to plead guilty to lesser state charges of soliciting women who were controversially labeled prostitutes.

Epstein ended up serving 13 months in a Florida jail during which he was allowed out six days a week to attend his plush business offices.

Senior Democrats have been lining up to call for Acosta to go. On Tuesday the party leader in the Senate, Chuck Schumer, accused the labor secretary of having let a serial sex trafficker “off easy”.

Schumer said: “This is not acceptable. We cannot have as one of the leading appointed officials in America someone who has done this.”

Others to call for Acosta to go include House speaker Nancy Pelosi, the most powerful Democrat in Congress, Tim Kaine, a senator from Virginia, and former vice-president Joe Biden, now running for the presidential nomination.

On Tuesday, Donald Trump gave his first comments since Epstein’s arrest. Speaking to reporters in the Oval Office, the president praised Acosta as an “excellent secretary of labor” said: “The rest of it we’ll have to look at very carefully but you are talking about a long time ago.”

Trump tried to minimize Acosta’s role in the 2008 plea deal, saying: “I hear there were a lot of people involved in that decision not just him.”

The Department of Labor is widely respected for its vital role in investigating, prosecuting and preventing human trafficking worldwide. Experts say any major cut to ILAB would be a direct threat to the US government’s ability to combat the sexual exploitation of children.

“A huge cut of this sort is bound to expose children to more risk of sexual trafficking,” said Kathleen Kim, a professor at Loyola Law School in Los Angeles who co-authored California’s law on human trafficking.

“An 80% reduction at ILAB will undoubtedly eliminate many of the US government’s anti-human trafficking efforts that have been critical in encouraging action by law enforcement.”

Kim said Acosta having granted the lenient plea deal to Epstein, combined with the proposed cuts to ILAB, made it entirely inappropriate that he continued in his current role.

“He should step down,” she said.

The battle over the future of ILAB is ongoing. Acosta’s proposed cuts were imported into Trump’s $4.7tn federal budget, released in March, which contains several Republican goals including extra money for the military and funding of the president’s beloved border wall.

The Democrats have responded with a 2020 House budget that passed in June. It would see ILAB resources expand to $122m.

“Congress ultimately makes the decisions about how money is spent and appropriated,” said Clark. “We will prevail and the bureau will not be shuttered if we can get this item through Congress.”