European authorities have waded into a brutal political feud transfixing Romania, accusing the prime minister, Victor Ponta, of systematic abuse of the country's constitution and undermining the rule of law in his campaign to unseat the country's president.

A 22-page report from the European commission highlighting Romania's failures to observe EU legal standards, obtained by the Guardian before being released on Wednesday, says the Ponta government has ignored the constitution, threatened judges, illegally removed officials from key posts, and tampered with the democratic system of checks and balances in order to try to secure the impeachment of President Traian Basescu.

Earlier this month, Ponta used his parliamentary majority to unseat Basescu, rushing through new referendum rules on impeachment and ignoring the country's supreme court verdict that the moves were unconstitutional.

The report says the government's commitment to democracy has been put in doubt. In unusually strong language, the commission described Romanian politics as highly polarised.

"However, this political context cannot explain the systematic nature of several actions. They raised serious doubts about the commitment to the respect of the rule of law or the understanding of the meaning of the rule of law in a pluralist democratic system. Political challenges to judicial decisions, the undermining of the constitutional court, the overturning of established procedures and the removal of key checks and balances have called into question the government's commitment to respect the rule of law and independent judicial review. The commission is, in particular, extremely concerned by the indications of manipulations and threats which affect institutions, members of the judiciary."

Brussels demanded that the Ponta government reverse what has been widely seen as an assault on rights and democratic procedures.

Basescu has been suspended from office as head of state pending a referendum at the end of the month. On Monday, the interim president, Crin Antonescu, a Ponta ally, moved to satisfy Brussels by reinstating referendum rules that make it more likely that Basescu will escape impeachment and remain in office.

The impeachment vote will need a turnout rate of half of the electorate plus one to be valid, increasing the likelihood that the referendum will be void.

A commission spokeswoman said on Tuesday that Ponta had written to Brussels promising to meet all the demands set by the commission president, Jose Manuel Barroso.

Romania has been in the EU since 2007, but remains subject to an EU monitoring regime because it is seen as highly corrupt and criminalised, with a dubious commitment to the rule of law.

The report complains that ministers and parliamentarians are rarely edged out of office even when prosecuted for or convicted of corruption or conflicts of interest and that parliament routinely blocks all attempts to investigate political sleaze.

The detailed report looks at the country's record on combatting corruption over the past five years, but focuses on the current crisis because of the Ponta government's record since coming to power in May.

The report says the Romanian government may not understand how a pluralist democracy works, indirectly suggesting the country is not fit to be an EU member.

The perceived trampling of democratic rights and procedures have put paid to Bucharest's hopes of ending the Brussels monitoring regime. The report says surveillance needs to be continued and a further verdict on democracy in Romania will be issued by the end of the year.

"Judicial independence and the separation of powers are fundamental building blocks of a democratic society," the report says. "In the coming months all political levels in Romania will need to demonstrate through their actions their commitment to these principles in order to restore confidence."