The film star has added her name to a 14,000-strong petition backing four residents at the Menie estate who face possible eviction to make way for the luxury hotel, housing and golf complex.
Narnia actress Swinton, who has a property in Nairn, accused the Trump Organisation of "bullying".
But the US tycoon's Scotland representative, George Sorial, responded by saying the actress was "ill-informed" and siding with "extremists".
Mr Trump has secured planning permission to build the golf course on an environmentally-sensitive stretch of coast.
Councillors have refused to rule out using compulsory purchase orders (CPOs) to remove residents from the earmarked land.
Four householders are refusing to sell their homes to make way for the development, which will include 500 houses and 950 holiday homes.
They have called on the council not to support the use of CPOs.
Swinton won Best Supporting Actress last year for her role in legal thriller Michael Clayton.
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