New York City Mayor Michael Bloomberg says a strike by the city's transit union is "morally reprehensible."
The union went on strike early this Tuesday morning after negotiations broke down with the state's transportation authority.
The walkout will shutdown the city's huge bus and subway network, and throw the daily commute of its seven million customers into chaos.
Mr. Bloomberg says he will ask a judge to take legal action against the union.
Contract talks between the two sides have deadlocked over such issues as wage increases and at what age new employees will be eligible to receive a full pension.
Union head Roger Toussaint calls the dispute a fight over whether "hard work will be rewarded with a decent retirement."
An emergency plan is in effect to prevent massive traffic jams on New York's streets.
Some information for this report provided by AP and Reuters.