PDVSA said in a statement it would respect existing contracts governing shared investments with Exxon, but reserved the right to break contracts whose terms allowed it.
"The legal actions carried out by the US transnational are unnecessary
...and hostile," the statement said.
The US oil firm said it could not immediately comment on the news.
Hugo Chavez, the Venezuelan president, had also shaken oil markets on Sunday with a broader threat to cut off oil supplies to the US.
Both Chavez and Rafael Ramirez, the oil minister, had also previously said the US company was no longer welcome to do business in Venezuela.
Ramirez also said on Tuesday that fellow Opec members had expressed solidarity with the South American nation in the fight and consulted with the oil producers group's lawyers on a defence strategy.
Meanwhile, other oil companies, including Chevron, France's Total, Britain's BP and Norway's StatoilHydro, negotiated deals with Venezuela to continue as minority partners in Orinoco projects.
ConocoPhillips and Exxon refused the new terms, and have since been in compensation talks with PDVSA.