(Adds source saying sacking has not formally happened yet, political context)
CARACAS/HOUSTON, Nov 29 (Reuters) - Venezuela has removed Rafael Ramirez, once a powerful oil minister and president of state oil company PDVSA, from his post as representative to the United Nations in New York, four sources with knowledge of the matter said on Wednesday.
The news would cement Ramirez' fall from grace under leftist President Nicolas Maduro, who had sent Ramirez to the United Nations in 2014 in a major demotion from his role as oil czar.
Sources say the spat between the two politicians has grown, especially after Ramirez recently published online opinion pieces slamming the management of PDVSA for allowing oil production to plummet and admonishing the government for not taking measures to improve Venezuela's tanking economy.
Ramirez was seen by some as angling to be a presidential candidate in next year's election, as rivalries among the Socialist Party grow amid an economic crisis and Maduro's unpopular government.
"He was fired last night," said a source with knowledge of the information, who asked not to be identified.
Two other sources said Foreign Minister Jorge Arreaza traveled to New York this week. Another source said Ramirez tried to fight back and negotiate but was unable to.
However, a separate source said Ramirez had not been formally notified of a removal and that he was working at the United Nations on Wednesday.
The Information Ministry did not immediately respond to a request for comment. Reuters was unable to immediately obtain comment from Ramirez.
Maduro this week launched an oil industry shake-up by naming a military officer to head PDVSA and promising an anti-corruption campaign to break up "mafias" that have stolen from the OPEC nation's coffers. Some of his comments in a fiery speech on Tuesday night appeared aimed at Ramirez' tenure.
Venezuela's struggling oil industry will not see an immediate impact from the removal of Ramirez, who was a close ally of late socialist leader Hugo Chavez and served as the oil czar for a decade starting in 2004. (Additional reporting by Corina Pons in Caracas, writing by Brian Ellsworth; Editing by Jonathan Oatis)