New York City’s campaign regulator has fined Mayor Bill de Blasio’s team nearly $48,000 for improper activity — including a $550 makeup artist for his family, and a plane ticket to fly his bi-racial son to a civil-rights rally in the nation’s capital.

In levying the fines, the Campaign Finance Board on Thursday afternoon repeatedly rejected explanations from de Blasio’s team that the actions complied with the city law — one of the strictest in the nation.

According to a 16-page Summary of Final Board Determination, de Blasio’s team improperly spent hundreds of thousands of dollars from his $13.6 million war chest, which includes nearly $4 million doled out in public dollars under the city’s matching-funds program.

Violations against de Blasio include improperly taking money, as well as accepting donations that exceeded legal limits, among others.

The campaign was fined for hiring makeup artist Gina Riggi to prepare de Blasio, his wife and children for an election- night victory party.

According to the report, De Blasio’s campaign team told the board the expense was justified. Prohibiting the spending was “simply incomprehensible,” the team said, because “in the age of television, it is general knowledge that persons planning to appear on television often obtain makeup services so that their appearance on camera will not be unflattering.”

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The board noted that “personal grooming” is banned under the law.

Also rejected was de Blasio’s billing the campaign for a $298.70 plane ticket to send his son, Dante, to a 47th anniversary rally in 2010 in honor of Martin Luther King Jr.’s “I Have a Dream” speech in 2010.

Dante — de Blasio’s biracial son who is now a student at Yale — played a starring role in his father’s winning campaign. In a famous ad, the teenager vouched for the candidate’s bona fides for black voters.

The expense was justified, because de Blasio’s son is “a visible manifestation of how the [c]andidate’s life experience was resonant to the spirit of the occasion,” the mayor’s campaign team said.

De Blasio was also fined for spending $321.97 on an Enterprise rental car and $236.52 at a Days Inn in Santa Clara, California, where his daughter attended college. De Blasio said he was there for “finance prospecting meetings,” though there was only one donation from a California resident during his April 2012 trip, according to the report.

Dick Dadey, head of the good-government group Citizens Union, said the campaign’s justifications don’t “pass the smell test.”

“The rationales show a level of creativity we’ve not seen before in explaining serious violations of our campaign finance law,” Dadey said Thursday. “It just defies belief and undermines trust in the truthfulness of his reality. I mean, come on.”

The campaign also hired Hilltop Public Solutions, $116,250 of which were for “improper post-election expenditures,” the board said.

In a statement, de Blasio spokesman Dan Levitan said, “While we strongly disagree with many of the CFB’s findings, we are pleased that the 2013 campaign audit is now complete.”