The reporters' move came after messages were distributed online with the name and picture of a female reporter of television channel 7, inciting hatred among the recipients and urging them to act against her wherever she is seen.
The media group said the action was considered a threat to freedom of the press and the work of the media. They urged the prime minister to take action against the movement as the threatened reporter reaffirmed that she is impartial.
Upon receiving the letter, the prime minister said she would follow up the case and said she welcomed the media to work freely.
Meanwhile, Pheu Thai Party spokesman Prompong Nopparit said the party disagreed with the action and is now investigating the origin of the message but said a third party may exploit the situation.
Mr Prompong said he would coordinate with the Ministry of Information and Communications Technology to block the dissemination of such messages.
In other incident, two men were hurt by some Red Shirt activists gathering outside the Parliament compound during the third day of the government's policy statement delivery after the pair laid a wreath protesting the work of House Speaker Somsak Kiatsuranond.
One of the injured, identified as Yuthabhum Tanleng, 34, was harmed when the Red Shirt protesters grasped the wreath, forcing him and a friend to run for their safety.