(CNN) Treasury Secretary Steve Mnuchin is opposing Democrats' request to disclose Secret Service costs related to travel by President Donald Trump and his family, instead delaying the disclosure until after the presidential election, a Democratic congressional aide confirmed to CNN.

The issue has become a point of contention as Democrats look to broker legislation with the Trump administration to move the Secret Service back to Treasury, its prior and original department. Negotiations are ongoing between the Service and Senate Democrats to try to resolve the issue, the aide said.

The Washington Post on Wednesday first reported Mnuchin's seeking to delay the spending disclosure.

Mnuchin agreed to requirements that the agency disclose the President's and his adult children's travel, according to the Post. But people with knowledge of the talks told the Post that Mnuchin has pushed back against Democrats' stipulation that such disclosures begin by 120 days after the bill's passage, as he wants them to start next year.

In a December letter to the Senate Judiciary Committee, Mnuchin strongly objected to the requirement, the paper reported. People monitoring Mnuchin's proposal told the Post that his insistence on reporting starting in 2021 probably aims to limit Democratic support.

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