ATHENS -- Greek workers were gearing up for May Day strikes Tuesday over ongoing austerity measures that have pushed the country deep into recession, days before elections in which the country's two ruling parties must convince voters of the need for fresh cutbacks.

The traditional May Day strike is expected to bring Greece to a standstill with hundreds of thousands of public and private sector workers walking off the job in commemoration of the labor movement, shuttering shops and closing most central and local government offices.

Public transport services in and around the capital, Athens, are expected to be disrupted by a partial walkout from transit workers, while a strike by one of Greece's seamen's unions will mean ferry services to the country's islands will be suspended.

Greece's two major umbrella unions--private-sector GSEE and public sector ADEDY--have called for a rally in the center of Athens Tuesday, while a separate group of left-wing protesters will hold their own demonstration nearby.

"This year's May Day strike and protest have taken on the characteristics of a special battle amid the continuing harsh, unjust, anti-social and neo-liberal measures," GSEE said in a statement. "Workers and the unions are girding for battle."

There are fears that violence could mar the normally peaceful protests, although police sources say they are expecting only a modest turnout on the streets.

Greece's economy is now in its fifth year of recession, made worse by waves of austerity measures the Greek government has taken to close a yawning budget gap and in exchange for two successive rescue packages from its European partners and the International Monetary Fund.

More than one in five Greeks is now jobless, and more than 60,000 retailers have closed in the past two years. On Monday, the latest data showed retail sales volumes in February plunged 11.8% in inflation-adjusted terms as consumer spending slumped and the Greek economy continued to deteriorate. Other data showed bank lending shrinking 4% in March.

Against that backdrop, Greek voters will decide Sunday whether to return Greece's two major parties--the Socialist Pasok party and the conservative New Democracy party--to power, whose first task will be to outline some EUR11.5 billion in further austerity measures demanded by the country's creditors in June.

The two parties, who have ruled in a fractious coalition government since November, look likely to secure just enough votes to form a majority in Greece's 300 member parliament--but with half the vote going to anti-austerity parties of the left and right.

"It looks that New Democracy and Pasok combined could breach, or come very close, to the 50% popular support threshold in the election. This means they will be able to form a coalition government," said a veteran senior socialist party official.

He added that New Democracy--which holds the lead according to the latest polls from 10 days ago--is expected to win "a minimum 30%" of the vote and Pasok to win "above 20%," an estimate shared by some New Democracy officials as well.

"New Democracy is pushing for a clear win, but internal polls suggest it will be difficult to achieve," a conservative party official adds. "Although (New Democracy party leader Antonis) Samaras believes an agreement with Pasok will be difficult, if the will of the Greek people is for a coalition government then they will have to co-exist, at least for the short term, so the measures in June get through parliament," he said.

Some 32 parties are contesting this year's elections, with eight to ten expected to clear the 3% threshold needed to enter parliament--up from five currently. Despite the plethora of parties, the campaign has been a subdued one, without the giant pre-election rallies that usually characterize Greek campaigns.

One reason: with anti-incumbent anger high and with verbal and sometimes physical attacks on members of parliament increasingly frequent, the two major parties have mostly chosen to forego their traditional big, outdoor gatherings of past years.

New Democracy will hold its final rally in Athens Thursday inside one of the city's main ceremonial venues. Pasok will hold its final rally Friday in Athens central Syntagma Square, but there are some fears that the protest could become a magnet for disaffected voters who are ready to punish the two main parties--both at the polls and maybe physically--to express their discontent over their policies.

"What I am most worried about is the anger," said Theodore Couloumbis, professor emeritus at the University of Athens. "People won't vote rationally, they will vote to punish."

-By Alkman Granitsas and Costas Paris, Dow Jones Newswires; +30 210 373 1774; alkman.granitsas@dowjones.com