Bersih 2.0, which challenged the ban in the High Court, will appeal the ruling, Ms. Abdullah said. “I don’t know where they got the idea we are a national security threat,” she said. “We are going to challenge this decision.”

A lawyer representing the group, New Sin Yew, said that under the edict, shirt wearers could be fined about $1,185. Some people have been briefly detained for wearing the shirts, he said, but he was unaware of anyone being prosecuted or fined.

A Malaysian government spokesman declined to comment on the case but insisted that citizens were free to speak their minds.

“The reality in Malaysia is that there is freedom of expression without fear of prosecution,” he said, speaking on the condition of anonymity. “Online and in print, the media is freer than it has ever been.”

The huge transfer of funds to Mr. Najib’s account has been reported to have come from companies linked to a sovereign wealth fund, 1Malaysia Development Berhad, or 1MDB. Mr. Najib set up the fund and is the chairman of its advisory board.

Mr. Najib has not publicly explained the source or purpose of the money, although he has denied wrongdoing and said that he took no money for personal gain.

Bersih 2.0 urged the prime minister to step aside while the unusual transactions were investigated.

Instead, Mr. Najib has used his authority to derail government investigations, including removing the attorney general before he could conclude his investigation and firing a deputy prime minister who questioned the transactions.