Tickets for the 7 November event cost $1,500 (£1,220) per head.
The gala was advertised as an “exclusive event for only 100 VIPs,” the SPLC said.
Mar-a-Lago cancelled the event after details about the gala were reported in news outlets at the weekend.
The company has not said why the group’s gala was cancelled. An Act spokesperson suggested negative media attention played a role in the decision.
“Regrettably, the Trump attorneys in New York caved to the Left’s bullying tactics and made a decision to cancel our event within hours of [news] articles coming out,” an Act for America spokesperson claimed in a statement.
The spokesperson added that the media had “falsely” claimed the organisation was a hate group.
Ms Gabriel said she did not blame “President Trump or the Trump family,” for the decision.
In her 2006 book the far-right activist wrote that “the Arab Muslim world, because of its religion and culture, is a natural threat to civilised people of the world, particularly Western civilisation.”
“Act pushes wild conspiracy theories about Islam in America and lobbies to pass anti-Muslim legislation throughout the country,” an SPLC spokesperson said.
“No individual, organisation or public official should profit from bigotry,” said Nihad Awad, the national executive director of the Council on American-Islamic Relations.
“We cautiously welcome the cancellation of Act for America’s hate event at Mar-a-Lago and urge other potential venues nationwide to consider the group’s history of Islamophobia and associations with white supremacist and racist organisations.”
The SPLC said the Mar-a-Lago gala had marked a departure from previous Act for America events.
“The group usually opens its conferences to anyone, advertising via mass email and social media six months in advance,” a spokesperson said.
According to the advocacy group, the annual gala is usually held at a Washington DC venue, around 11 September.
The Mar-a-lago gala’s ticket prices were around 400 per cent more expensive when compared to previous years, where they cost between $250 (£203) and $300 (£244).
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