The charges, which include "espionage for Israel, insulting religious sanctities and propaganda against the Islamic republic", were brought last week.
Junior foreign minister Bill Rammell said he was "very concerned" over the charges, which he noted could attract the death penalty.
"The Iranian government appears to be increasingly using vaguely worded charges of this nature to target human rights defenders and religious minorities," Rammell said in a statement.
"It is hard not to conclude that these people are being held solely on account of their religious beliefs or their peaceful exercise of their right to freedom of expression and association."
The group had been forced to wait eight months before being notified of the charges against them, he said: they did not have access to their lawyers, and their lawyers had not been given access to their case files.
"We have also received disturbing reports of systematic discrimination against and harassment of Bahais on the grounds of their religion," he said.
"Iran should also uphold fully the right to adopt and practise a religion of choice, and end discrimination against the Bahai community," said Rammell.
He called on Tehran to ensure that any trial was fair and transparent, adding.
Followers of the Bahai faith, founded in Iran in 1863, are regarded as infidels and have suffered persecution both before and after the 1979 Islamic revolution.
Bahai teachings emphasise the underlying unity of major religions, with history having produced a succession of divine messengers, each of which founded a religion suitable for the times.
Bahais consider Bahaullah, born in 1817, to be the last prophet sent by God. This is in direct conflict with Islam, the religion of the vast majority of Iranians, which considers Mohammed to be the last prophet.
