Law Asia, a regional lawyers' association, said it had sent four members in response to an open invitation the government issued two days after President Abdulla Yameen imposed a state of emergency.
That followed a Supreme Court order, later rescinded, to release political prisoners and reinstate sacked lawmakers a move that would have cost Yameen his majority in parliament.
The president has overseen a major crackdown on dissent in recent years, jailing a series of prominent critics including the opposition leader and sacking MPs who defected from the ruling party.
Earlier this month Yameen sacked the chief justice and another senior judge before imposing emergency rule, sparking international condemnation.
The crisis has hit the image of the Maldives as a peaceful holiday paradise, although it has had little impact on life away from the capital in the upmarket resort islands popular with honeymooners.
The four lawyers were detained on Sunday when they arrived at Male international airport, where they were held and subsequently deported, Law Asia said.
"By such action, the government of Maldives deprived itself of the benefit of an independent and impartial assessment by a fact-finding team not sponsored by any individuals, parties or organisations in the Maldives," it said.
Law Asia said they had been trying for more than two weeks to arrange special visas before deciding to send the delegation after informing the immigration authorities.
Separately, Yameen's niece Dunya Maumoon resigned late Tuesday as health minister.
She had been under pressure to resign since Yameen ordered the arrest of her father, ex-president Maumoon Abdul Gayoom.
The 80-year-old was president for 30 years until the country's first democratic elections in 2008 and was initially see as the power behind the throne until be became estranged from his half brother and backed the opposition.
He was arrested on a charge of trying to topple the government hours after the emergency was declared.
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