Tusk, the leader of Poland's largest opposition bloc, the Civic Coalition (KO), and the opposition's joint candidate for the new prime minister, made the declaration at a news conference in Warsaw on Tuesday, Polish state news agency PAP reported.
Tusk, a former prime minister, told reporters: "I said during the election campaign that our aim would be to put the country back in order after the Law and Justice (PiS) government. The first step must be to hold them accountable."
By the end of the year, Poland's new parliament will establish three investigative commissions to probe "irregularities" under the PiS government, Tusk said.
The panels will probe a recent cash-for-visas scandal, the government's alleged abuse of the Pegasus surveillance spyware, and measures taken to hold the 2020 presidential election as a postal vote amid the COVID-19 pandemic, the PAP news agency reported.
Poland's governing conservatives have denied any wrongdoing.
Tusk, a former top European Union official, told reporters that the commission into the 2020 postal ballot could be set up next Tuesday.
He also said that opposition groupings had a sufficient majority in parliament to bring the governor of Poland's central bank (NBP), Adam Glapiński, before the State Tribunal, private broadcaster RMF FM reported.
In addition, Tusk declared that the opposition would seek to dismiss members of the recently established "state commission into Russian influence in Polish politics." They were appointed by the previous parliament.
Tusk also said the opposition groups would soon submit bills to relax abortion rules, while this week MPs would consider a citizens' bill backed by the opposition to ensure state funding for in vitro fertilisation.
Poland to appoint new gov't
Poles elected a new set of 460 MPs and 100 senators when they went to the ballot box last month.
Polish President Andrzej Duda this month named Mateusz Morawiecki, who has led Poland's government since 2017, as prime minister-designate, tasking him with forming a new Cabinet.
The ruling conservative Law and Justice (PiS) party won Poland's October 15 election, but lost its parliamentary majority and looks unlikely to stay in power for a third consecutive term.
Meanwhile Tusk has already chosen most candidates for ministerial roles in his future Cabinet, according to the Rzeczpospolita newspaper.
A bloc of opposition parties led by Tusk's Civic Coalition last week secured a resounding victory in Poland's new parliament during its first key vote to elect a house Speaker.
On November 10, these opposition groups, which also include the rural-based Polish People's Party (PSL), the centre-right Poland 2050 group and the Left party, signed an agreement to form a coalition government, pledging to restore the rule of law, promote green energy and relax abortion rules, among other policies.
Tusk was Poland's prime minister from 2007 to 2014.
(pm/gs)
Source: PAP, RMF24