The order to expel New York Times bureau chief Declan Walsh from Pakistan came on the eve of the crucial general elections in the country.
"The expulsion of Declan Walsh shows just how much the authorities fear independent media coverage," said Bob Dietz, of Protect Journalists.
"The vagueness and the late night delivery of the expulsion order smack of a need to intimidate foreign and local journalists on the eve of historic elections that could herald the growth of democracy in Pakistan. Instead, Walsh's expulsion only mars the event, and undercuts hopes for a free press," Dietz said in a statement.
Later this month, the media watchdog plans to publish a report analysing the state of press freedom in Pakistan.