FIRST ON FOX: Rep. Darrell Issa, R-Calif., is expected to send a letter to California Gov. Gavin Newsom, Sen. Alex Padilla, D-Calif., Senate Majority Leader Chuck Schumer, D-N.Y., and Senate Minority Leader Mitch McConnell, R-Ky., on Monday afternoon expressing concern over Newsom’s recent appointee to replace the late Democrat Sen. Dianne Feinstein.

Newsom tapped Laphonza Butler, the president of EMILY's List – a Democratic political action committee (PAC) dedicated to electing pro-abortion Democratic women to office – for the vacant interim Senate seat late Sunday evening.

However, Butler's home address is listed in Silver Spring, Maryland, and Issa is questioning the constitutionality of her ability to take office while residing in a different state than the one she will represent.

"We're not talking about the question of majority, we're talking about 38 million Californians who have an absolute right to have somebody who puts California first – not who puts the District of Columbia first or Maryland, where she's a resident, first," Issa told Fox News Digital in an interview Monday.

NEWSOM NAMES LAPHONZA BUTLER, FORMER KAMALA HARRIS ADVISER, TO FILL FEINSTEIN'S VACANT SENATE SEAT

Issa, Newsom and Butler split image

Rep. Darrell Issa, left, California Gov. Gavin Newsom and EMILY's List president Laphonza Butler (Fox News)

"It's not that he couldn't find somebody," he continued. "Instead, [Newsom] chose the most progressive African American woman he could find, seemingly for political purposes."

Issa expects he will have a handful of co-signers on the letter.

Newsom's office told Fox News Digital that Butler moved to the suburbs near Washington, D.C., when she became EMILY's List president in 2021, and that she has a house in California. The governor's office added that Butler will re-register to vote in California before she is sworn in.

"The quid pro quo of agreeing to pay your California taxes in return for becoming a senator is not an acceptable bargain," Issa said. "That's a privilege the rest of us don't get."

According to California law, to be eligible for a Senate bid, a person must be a U.S. citizen, a resident of California, and a registered voter in the state. 

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Gavin Newsom and Laphonza Butler

California Gov. Gavin Newsom on Sunday announced that Laphonza Butler would replace Dianne Feinstein in the Senate. (Tayfun Coskun/Anadolu Agency via Getty Images)

Butler's EMILY's List biography had her residence listed as Silver Spring, Maryland, earlier Sunday evening, but it was removed from the profile shortly after it was announced she would be appointed to the position. An FEC filing from Aug. 31 also showed a Maryland address.

The seat is a highly contested one ahead of the 2024 election, and the governor's decision has significant implications for the deep blue bastion that is seen as the poster child for Democratic policies.

Butler will finish out the remainder of Feinstein's term in Washington, D.C., ahead of the 2024 election. In a statement, the governor described Butler as an "advocate for women and girls, a second-generation fighter for working people, and a trusted adviser to Vice President Harris."

"As we mourn the enormous loss of Sen. Feinstein, the very freedoms she fought for – reproductive freedom, equal protection, and safety from gun violence – have never been under greater assault," Newsom added. "Laphonza will carry the baton left by Sen. Feinstein, continue to break glass ceilings, and fight for all Californians in Washington, D.C."

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Democratic California Gov. Gavin Newsom

California Gov. Gavin Newsom (MediaNews Group/East Bay Times via Getty Images)

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Butler thanked Newsom for the appointment in a statement on Monday.

"I am honored to accept Gov. Newsom’s nomination to be a U.S. Senator for a state I have long called home," she said.

Butler will be the only Black woman serving in the U.S. Senate and the first openly LGBTQ+ lawmaker to represent the Golden State in the upper chamber.

Other top Democrats vying for the seat in 2024 include Democrat Reps. Adam Schiff, Barbara Lee and Katie Porter. 

Fox News' Houston Keene and Anders Hagstrom contributed to this report.