This post has been updated.

NEW YORK — On the eve of a crucial Democratic presidential primary here, Bernie Sanders accused rival Hillary Clinton on Monday of appearing to violate campaign finance laws with her expansive use of a joint fundraising committee set up last year with the national party.

The controversy seemed to further sour relations between the two Democratic hopefuls at a point in the campaign where their patience with one another had already worn extremely thin, as evidenced by their testy debate in Brooklyn this week.

In a letter to the Democratic National Committee, a lawyer for Sanders said the joint committee, which can accept far larger donations than Clinton’s campaign, appeared to be improperly subsidizing her campaign by paying Clinton staffers with funds from the committee and cited other alleged violations as well.

Later Monday, Clinton’s campaign manager said Sanders’s attacks had “gotten out of hand.”

“As Senator Sanders faces nearly insurmountable odds, he is resorting to baseless accusations of illegal actions and poisoning the well for Democratic candidates up and down the ticket,” said Robby Mook, Clinton’s campaign manager.

Mook also took aim at Sanders’s campaign for sending out a fundraising solicitation highlighting its accusations, a tactic Mook called “shameful.”

Sanders spokesman Michael Briggs later brushed off Mook’s comments, saying his statement included “rhetorical smoke” but did not address the underlying issue.

The Sanders letter cited a February report by The Washington Post that detailed the Clinton campaign’s expansive use of a joint fundraising committee it set up last year with the DNC and 32 state party committees.

Wealthy donors can give $356,100 annually to the Hillary Victory Fund, the largest joint fundraising committee of its kind. The contributions are then distributed proportionally between the campaign, the DNC and state parties.

But The Post found that before distributing its proceeds, the victory fund has spent millions on direct mail and online ads seeking small donors to support Clinton’s campaign. The victory fund also sponsors Clinton’s online store, allowing donors who have already given the maximum to her campaign to purchase Hillary lapel pins, caps or car magnets, with their money benefiting the party.

The fund functions as an operation embedded within the Clinton campaign, which has been reimbursed $2.6 million for salaries and overhead. Its treasurer is Elizabeth Jones, the Clinton campaign’s chief operating officer.

In his complaint to the DNC, Sanders counsel Brad C. Deutsch said that it appears that the victory fund is using contributions from “big-dollar” donors to finance activities benefiting Clinton. He said that the fund could be subsidizing Clinton’s prospecting for new donors by finding supporters that her campaign is able to tap again and again.

Deutsch said Sanders’s campaign is concerned that the DNC and state parties are making illegal in-kind contributions to Clinton’s campaign through the committee.

A spokesman for the DNC declined to directly address Sanders's allegations.

“The DNC offered to engage in the same joint fundraising efforts with all the major presidential candidates early in the cycle and we welcome the efforts of the candidates to help raise money for the DNC and state parties now to ensure we can build out the infrastructure to win in November,” said Mark Paustenbach, the DNC’s national press secretary.

What it looks like on the ground in New York for the primary election

MANHATTAN, NY - Winning the New York primary, former Secretary of State Hillary Clinton speaks to a packed room of supporters during the victory party at the Sheraton Hotel in midtown Manhattan, New York on Tuesday April 19 2016. (Melina Mara/The Washington Post)

DNC officials noted that expenses incurred by the victory fund that result in donations for Clinton have to be paid by her campaign, so the party is not subsidizing her activities.

Asked why the Sanders campaign had directed its concerns to the DNC rather than the Federal Election Commission, which has jurisdiction over such complaints, Briggs called Monday’s letter “a first step.”

"The first step is to go to the DNC because they are a party to this arrangement," Briggs, the Sanders spokesman, said.  "This is the first step, and we'll see what happens."

Anne Gearan contributed to this report.