ACR X NON ADHERENCE TO ATC CLRNC NON ADHERENCE TO FAR. EXCEEDED 250 KTS BELOW 10000 FT. PLTDEV.

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2 ACFT DEPART JFK ARPT RTED OVER THE SAME FIX. INITIALLY THEY WERE ABOUT 5 MI APART. I TURNED THE FIRST ACFT ON COURSE AND DELAYED THE SECOND ONE (ACR X) A COUPLE OF MI TO BUILD A LITTLE MORE SPACING ON THE RTE. THEY WERE BOTH HVY JETS. AFTER I TURNED ACR X ON COURSE; IT LOOKED LIKE HE WAS INCREASING HIS SPD SO I ADVISED THE PLT NOT TO EXCEED 250 KTS UNTIL ADVISED. THE PLT ANSWERED WITH A CORRECT READBACK. EVEN THOUGH THE PLT ACKNOWLEDGED THE 250 KT SPD RESTRICTION; HE WAS STILL INCREASING SPD AND CATCHING THE LEADING ACFT. AT THIS POINT I ASKED ACR X TO SAY HIS AIRSPD; HE SAID 'SLOWING TO 250 KTS.' I THEN ASKED ACR X HOW HE COULD BE SLOWING TO 250 KTS WHEN HE WAS NOT SUPPOSED TO HAVE EXCEEDED 250 KTS! (I DON'T REMEMBER HIS REPLY). I ALSO TURNED ACR X OFF THE RTE BECAUSE I WASN'T SURE IF I WOULD BE ABLE TO MAINTAIN SEPARATION. AFTER ABOUT 30 SECONDS IT WAS STILL OBVIOUS THAT ACR X WAS STILL FASTER THAN THE LEAD ACFT. I AGAIN ASKED THE PLT TO SAY HIS AIRSPD; HE REPLIED '270 KTS!' I THEN ASKED THE PLT WHY HE WAS NOT COMPLYING WITH MY CTL INSTRUCTIONS AND IF THERE WAS SOME SORT OF PROBLEM. HE SAID 'NO PROBLEM BUT I CAN'T IMMEDIATELY SLOW FROM 310 KTS TO 250 KTS.' DURING THIS WHOLE INCIDENT; ACR X WAS WELL BELOW 10000 FT AND ONLY ABOUT 2-3 MI OFF THE S SHORE OF LONG ISLAND. THIS IS NOT THE FIRST TIME A FOREIGN ACR HAS VIOLATED THIS REG.