ATHENS, Greece (AP) — Greece's leftwing prime minister defended his unpopular pension reform plans Tuesday, pledging to avoid new cuts, as protests against the creditor-demanded measures escalated.

Alexis Tsipras told a special parliamentary session that the financially struggling country's pension system faces collapse unless swift corrective action is taken.

He insisted that the reforms will see no new reductions in core pensions — which have been repeatedly slashed since the start of Greece's financial crisis.

The pension overhaul has been demanded by Greece's bailout creditors, whose rescue loans have kept the country afloat since mid-2010.

The proposed changes will lead to large increases in social security contributions, mostly affecting self-employed professionals and farmers, who say that they will end up paying more than three quarters of their income to pension funds and tax authorities.

Unions representing groups as disparate as lawyers, doctors, police and fishermen are protesting the reforms, while farmers are using thousands of tractors to block highways across the country.

Conservative opposition leader Kyriakos Mitsotakis accused the year-old government of "sacrificing future generations to gain popularity today," and warned in Parliament that the measures will increase tax evasion and non-payment of social security contributions.

Ferry crews walk off the job on Wednesday and Thursday — their second 48-hour strike in a week — while lawyers are also on strike.

State hospital employees scuffled with police outside the finance ministry Tuesday, and thousands of workers took part in two peaceful evening marches to Parliament, called by the civil servants' union and a Communist-affiliated group.

Farming associations in central Greece voted to step up closures, with four-hour daily blockades at highways and ports, while protest groups in southern and northern Greece are planning similar action.

Elsewhere, flower growers disrupted traffic at a highway toll station north of Athens, while engineers in the northern city of Thessaloniki used sheets of plasterboard to block the entrance of a pension fund building.