Palestinian Authority police on Monday detained Jamal Hlaihel over a Facebook post deemed critical of the government, Human Rights Watch reported Tuesday.
Hlaihel is the fourth Palestinian to be arrested recently for criticizing the Ramallah-based government.
Two journalists and a university lecturer were also detained for newspaper articles and Facebook posts that the authorities said were slanderous. The academic remains behind bars.
"We need laws to clarify the rights of journalists, protecting their work and completely removing the threat of detention and interrogation," said Abdel Nasr al-Najjar, head of the Palestinian Journalists Syndicate.
"It's unacceptable that detention for any period should be involved for any charge not related to security," he told Reuters.
While Palestinian journalists have been detained before, the arrest of four people within a week has raised concerns in the West Bank about media rights.
Yousef al-Shayeb was arrested last month after he published an article reporting on alleged corruption in the Palestinian foreign ministry and suggesting that officials had collaborated with Western intelligence agencies.
He was released on bail on Monday after spending eight days in prison and faces prosecution over his story.
Lecturer Ismat Abdul Khaliq remains in jail for comments she posted on Facebook in which, prosecutors say, she called for the ousting of President Mahmoud Abbas, branding him a "traitor" and a "fascist".
Journalist Tariq Khamis was detained and interrogated on Sunday after he discussed her case on his own Facebook page.
"The authorities are afraid of journalism," Khamis told Reuters, saying he had been questioned five times in the past. "I was questioned on my work as a journalist, and they confiscated the files on my laptop."
Government representatives said Shayeb did not provide sufficient evidence for his accusations and argue that all three cases represent possible slander.
"Freedom of expression stops at defamation," said Adnan Dmeiri, spokesman of the security services in the West Bank. "It's natural that any citizen can respond to insults and baseless accusations with a lawsuit."
The Palestinian Authority, which has struggled to maintain support as its bid for statehood flounders, receives strong political and financial backing from the West. It recently became a member of the United Nations cultural and education body, UNESCO, which stresses press freedom.
The controversy has flared just as the PA is sponsoring an event to reward press freedom, with a prize due to be given out next month. However, following the recent detentions, the Journalists Union says it will boycott the occasion.