The complaint says the ECB's plan, which pumps money into the financial system much the same way as the U.S. quantitative easing program, oversteps its mandate and violates a ban on it funding governments.
The ECB's Outright Monetary Transactions (OMT) program, announced by President Mario Draghi in September 2012 at the height of the sovereign debt crisis and as yet unused, is widely credited with pulling the euro zone back from the brink.
"The ECB has to quickly assess what repercussions the ruling will have for the range of tools available to calm markets," said Christian Schulz, senior economist at Berenberg. "Ironically, depending on the exact decision, the court may have made a much more wide-ranging quantitative easing program at the ECB more likely."
The euro traded up 0.5 percent to 139.47 yen. The dollar also advanced against the yen, after regaining ground from the initial sell-off after the jobs data. In midday New York trade the greenback rose 0.2 percent to 102.32 yen.
In contrast to the weak U.S. jobs data was an upbeat report from Canada which showed a bigger-than-expected increase in its January payrolls.
"I think this increase in employment in January dampens expectations of the possibility of the Bank of Canada having to cut rates. But certainly with inflation remaining low, there's no pressure to start moving rates higher," said Paul Ferley, assistant chief economist at Royal Bank of Canada.
The U.S. dollar fell 0.3 percent to C$1.1037. It had been as low as C$1.0964, its weakest point in 2-1/2 weeks.
Sterling extended its gains against the greenback as the trading session wore on, climbing 0.5 percent to $1.6403 , its best level of the week.
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