Turkish journalist Sedef Kabas risks up to four years in jail for allegedly insulting President Recep Tayyip Erdogan.
Police detained her in the early hours of Saturday morning, and a court ordered her to remain in jail pending a trial.
Kabas' lawyer Ugur Poyraz said they would appeal the "unlawful" decision on Monday.
"We hope Turkey can return to rule of law soon," Poyra said.
Kabas did not name Erdogan directly. However, the authorities object to a proverb that she used during a show on Tele1 television and later tweeted.
"When the ox comes to the palace, he does not become a king," Kabas said. "But the palace becomes a barn."
Ministers outraged by remarks
Erdogan spokesperson Fahrettin Altun called Kabas "immoral" and "irresponsible."
"The honor of the presidency's office is the honor of our country. ... I condemn the vulgar insults made against our president and his office," he wrote.
Turkey's justice minister, Abdulhamit Gul, wrote on Twitter that Kabas will "get what she deserves" for her "unlawful" remarks.
The country's broadcast regulator, RTUK, meanwhile, started an investigation into Tele1 for "unacceptable statements targeting our president."
Tele1's chief editor, Merdan Yanardag, sharply criticized the arrest.
"Her detention overnight at 2 a.m. because of a proverb is unacceptable," he wrote on Twitter. "This stance is an attempt to intimidate journalists, the media and society."
Thousand convicted for insulting Erdogan
Insulting the president carries a jail sentence of between one and four years.
Since Erdogan became president in 2014, 35,507 cases of insulting the president were filed and there were 12,881 convictions.
Kabas had previously been charged after she posted criticism of a government-appointed judge who dropped a corruption probe against Erdogan and other politicians. She was later released.
The Turkish journalists union called the arrest a "serious attack on freedom of expression."
Reporters Without Borders places Turkey at 153 out of 180 countries in their press freedom index.
