Mohammed al-Yemeni, a freelancer for several media outlets in Yemen, was killed by rebel sniper fire on Monday in Taez, the union said in a statement carried by the official sabanew.net website.
Three other cameramen were wounded in the gunfire, the statement added, identifying them as Naef Wafi, Haikal al-Uraiki and Abdulqawi al-Azzani.
The union urged all warring parties in the country to "stop their systematic targeting of journalists."
Last month, a rebel sniper shot dead Ahmed al-Shaibani, a cameraman working for the government-run Yemen TV channel, while he was covering clashes in Taez.
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His killing drew condemnation from international media watchdogs.
Yemen has been hit by unrest since the Shiite Huthi rebels and allied loyalists of former president Ali Abdullah Saleh overran the capital Sanaa in September 2014 and forced the government to flee south.
The violence significantly increased after a Saudi-led coalition launched a military campaign against the rebels one year ago.
Taez, which was besieged by the rebels for months, has been the scene of deadly battles with some 200,000 civilians caught up in the fighting.
Pro-government forces backed by a Saudi-led coalition managed to break the rebel siege of the southwestern city this month.
The World Health Organization says fighting in Yemen has killed almost 6,300 people, half of them civilians, since March 2015.