The move comes a week after the Law and Justice (PiS) government lost a diplomatic campaign to oust rival Donald Tusk -- a former Polish premier from the PO -- from his current post as European Council president.
The PO said it would lodge the motion next week. It has no chance of succeeding, since the PiS enjoys an absolute majority in parliament.
"For 17 months now, the government of (Prime Minister) Beata Szydlo has been demolishing Poland," PO lawmaker Slawomir Neumann told reporters.
"It's been demolishing democracy, the state of law, especially civil liberties. It's been attacking self-governing local institutions, the independent judiciary," he added.
Since coming to power in November 2015, the PiS has introduced several controversial reforms, including an overhaul of the constitutional court and moves to increase state control over public broadcasters.
"Over the course of the last few days and weeks, it discredited Poland on the world stage," Neumann added, referring to last week's clash at the Brussels summit of EU leaders.
The bloc's leaders voted by 27 to one to give Tusk a fresh two-and-a-half-year term -- with only Szydlo voting against.
The outcome led Foreign Minister Witold Waszczykowski to accuse the European Union of "cheating" and announce a "negative" policy towards Brussels.
Fellow opposition parties, Nowoczesna and the PSL, said they would back the motion of no confidence.
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