By RANA F. SWEIS DEC. 7, 2014

AMMAN, Jordan — Zaki Bani Rushaid, the provocative deputy head of the Muslim Brotherhood in Jordan, has never been shy with his opinions.

For years, Jordan did nothing as he railed — often on nationwide television — against Jordan’s “meager” political reforms and what he sees as continued attempts to cozy up to the United States, which he calls “the cause of tyranny in the Middle East.” Despite his high profile, the kingdom appeared not to see him, or the Brotherhood, as a threat.

Then, on Nov. 17, Mr. Bani Rushaid took to his Facebook page with a new complaint, inveighing against the United Arab Emirates, which had recently branded the Muslim Brotherhood movements as terrorist groups. Among his accusations: that the Emirates plays the role of the “American cop in the region,” “supports coups” and is a “cancer in the body of the Arab world.”

Within days, he was behind bars, accused under a recently strengthened antiterrorism law for “acts harmful to the country’s relations with foreign countries.” Last week he lost an appeal for bail, and he is now awaiting trial and a possible sentence of at least two and a half years in prison.

The reason for the government’s sudden shift, analysts say, was that he crossed a political line by lashing out at the Emirates, an important ally of Jordan’s and one of several countries in the region, including Egypt and Saudi Arabia, that are on a campaign to wipe out the Brotherhood.

At least for the moment, analysts do not expect Jordan to join the Egyptians and the Saudis in cracking down hard on the Brotherhood, which has long operated legally in Jordan, where it has its own political party.

Instead, they see the detention of Mr. Bani Rushaid, and the earlier detention of a lower-level Brotherhood official, as a warning that the monarchy’s patience will extend only so far. (The other official was taken into custody after harshly criticizing Jordanian authorities for what he suggested was a tepid response to Israel’s latest offensive in Gaza.)

“Bani Rushaid’s latest criticism of the Emirates was an opportunity for authorities to finally detain the most important figure inside the Muslim Brotherhood and send the group a message to keep their mouth shut,” said Marwan Shehadeh, a political analyst in Amman.

The detentions shocked many in the country, where the Brotherhood has mainly been spared the roundups that were common in Egypt before the Arab Spring and are again now that the generals have wrested back control from that country’s branch of the Brotherhood.

Already, 200 lawyers in Jordan have signed up to represent Mr. Bani Rushaid in what one of his primary lawyers, Abdul Qader Khatib, said was mainly a symbolic gesture of support — and a rejection of what many see as a whittling away of civil rights as Jordan’s leaders have become increasingly jittery over the rise of the Islamic State on its borders, in both Syria and Iraq.

In the past seven months, prosecutors have detained dozens of Jordanians under the amended antiterrorism law, accusing them of crimes that included joining terrorist groups or promoting them on the Internet. Some of those in custody acknowledge discussing violent Islamist movements on the Internet, though they contend that does not constitute support.

But the detention of Mr. Bani Rushaid, and the implied challenge of the Brotherhood, seems to be something quite different from the wider crackdown. In his case, analysts said, it appears to be tied to Jordan’s increasing dependence on the Emirates and other Sunni monarchies that not only are helping keep its troubled economy afloat with infusions of aid, but are also banding tightly together as the Islamic State tries to destroy the status quo in the Middle East.

Jordan’s government spokesman, Mohammad Momani, denied that the authorities went after Mr. Bani Rushaid because of their relationship with the Emirates, saying it was instead because he broke the amended security law by speaking out against a friendly country.

Critics of the detention, however, point out that speaking against the United States has not landed anyone in jail. And analysts note that the Emirates has a particular hold on Jordan, promising in 2011 more than a billion dollars in grants over five years and, in the first half of this year alone, providing more than $70 million to care for the Syrian refugees in Jordan who are straining the Jordanian budget.

The Emirates also hosts about a quarter of a million Jordanian workers, whose remittances are a major source of cash for their families at home.

The Emirates has also made clear its view of Islamists of all stripes, playing a prominent role in campaigns against them across the region. Besides dismantling domestic Islamist groups, the country underwrote the military in Egypt in its fight against the Muslim Brotherhood and, like Jordan, is participating in the international fight against the Islamic State.

“The authorities could not remain idle against Bani Rushaid’s angry remarks that could have been interpreted wrongly by its allies Abu Dhabi, Riyadh and Cairo which all have blacklisted the Muslim Brotherhood, let alone the catastrophic economic consequences on Jordan,” a political columnist, Mohammad Abu Rumman, wrote in Al Ghad, an independent daily newspaper, soon after Mr. Bani Rushaid’s detention.

No matter the cause, Jordan’s rare challenge to the Brotherhood has raised eyebrows, with front-page reports prominently mentioning the group’s history of relative moderation.

The Brotherhood, Jordan’s largest opposition movement, is known for passionately pushing for democratic reform to diminish the relatively unchecked power of the king.

But it has not called for the overthrow of the monarchy, not even during the headiest days of the Arab Spring.

And although the government is accused of unfairly structuring elections so the number of Islamists in Parliament is limited, it has allowed the Brotherhood to take part. (The group, nonetheless, boycotted the last parliamentary elections, saying that the election law made it impossible for its members to compete on an equal basis with the king’s loyalists.)

As the controversy swirls around him, Mr. Bani Rushaid has remained defiant, threatening to sue the prime minister and others for slander. As a result, he is now being denied access to newspapers while in jail as punishment.

“Zaki’s detention is politically motivated, and under the Constitution, freedom of expression is guaranteed,” said Mr. Qader Khatib, the lawyer on his defense team.

“What he has been accused of, which is expressing his opinion on social media, goes against the Constitution.”

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