Services across the country have ground to a halt as Greeks walk off the job in a massive general strike that canceled flights, ferries and public transport, shut down schools and pharmacies, and left public hospitals with emergency staff.

Unions called Thursday's strike to protest pension reforms that are part of Greece's third international bailout. The left-led government is trying to reform the country's ailing pension system by increasing social security contributions to avoid pension cuts. But critics say the reforms will lead many to lose two-thirds of their income to contributions and taxes.

Opposition to the reform has united a disparate group of professions, including farmers, artists, taxi drivers, lawyers, doctors, engineers and seamen among others. A heavy police presence was deployed in Athens ahead of planned demonstrations.