Juhel Miah had flown to Reykjavik, Iceland, with the party from Llangatwg Community before boarding an onward flight to New York.
But before the plane took off on 16 February, he was escorted off by security staff.
BBC Wales has asked the US Embassy in London to comment.
Neath Port Talbot council has written to the US Embassy to "express its dismay" at the treatment of Mr Miah, who the local authority said had a valid visa to travel.
The school trip continued as planned but Mr Miah's removal left pupils and colleagues "shocked and distressed," a spokesman said.
"We are appalled by the treatment of Mr Miah and are demanding an explanation.
"The matter has also been raised with our local MP."
The council confirmed Mr Miah has a British passport and does not have dual nationality. His family's ethnic background is Bangladeshi.
The Foreign and Commonwealth Office said it was "providing support to a British man who was prevented from boarding a flight in Reykjavik".
Mr Miah, who teaches maths at the 700-pupil school, was also denied access to the US Embassy in Reykjavik, the spokesman added.
"No satisfactory reason has been provided for refusing entry to the United States - either at the airport in Iceland or subsequently at the embassy.
"Understandably he feels belittled and upset at what appears to be an unjustified act of discrimination."
On 27 January, US President Donald Trump signed an executive order halting all refugee admissions and temporarily barring people from seven Muslim-majority countries, sparking numerous protests and legal challenges.
A week later a federal judge in Seattle suspended it nationwide - a ruling which was later upheld at an appeals court hearing in San Francisco.
Mr Trump is now considering a revised plan.
Abdul-Azim Ahmed, assistant secretary general of the Muslim Council of Wales, said he was "deeply troubled" by the incident.
"What we do know is quite troubling and in the context of a school trip and the children being left with one less teacher because of this," he said.
"This is the latest in a series of incidents where Muslims have been denied entry to the US which date before even Trump was elected."
The school party returned to the UK on Monday after the week-long trip.

He had been facing charges of genocide during one of the most brutal periods in Guatemala's civil war.
Doctors said he was not able to understand any charges against him.
The medical report will affect two separate trials where he is charged with ordering the murder of hundreds of farmers and over 1,000 Mayan Indians.
General  Rios Montt was found guilty of genocide and war crimes two years ago, and sentenced to 80 years in prison.
The main charges were that he and his former intelligence chief ordered the army to carry out 15 massacres of Ixil Maya indigenous people in Quiche in northern Guatemala, in which around 1,700 Indians were killed.
However, a high court then threw out the charges on procedural grounds and ordered a retrial.
Another trial began in January but ended after the judge was rejected for having made public opinions about genocide in a student thesis.
A new trial was set for July. This may now not take place because of the medical examiner's report declaring the ex-leader mentally incompetent.
A Muslim teacher from Neath Port Talbot has been denied entry to the United States while on a school trip.
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A former Guatemalan general, Efrain Rios Montt, who ruled the country briefly in the 1980s, has been found mentally incapable of standing trial.