A judge's controversial decision to reduce the prison sentences of three mainlanders in line with the treatment given to foreigners is to be challenged by the Department of Justice in a court battle on Monday. Director of Public Prosecutions Grenville Cross, SC, will argue in the Court of Appeal that the approach taken by District Court judge Wesley Wong Wing-fai was wrong. He will argue that criminals from the mainland should not be allowed to benefit from a legal principle that has allowed some foreign offenders to receive more lenient sentences. The case is to be heard by three Chinese judges: Chief Judge Arthur Leong Shiu-chung, Mr Justice Woo Kwok-hing and Mr Justice Peter Cheung Chak-yau. Mr Cross, representing the Secretary for Justice, will ask the court to review and increase the sentences imposed on three defendants involved in two separate cases in September. The issue of sentence reductions for foreigners sparked controversy in August when the Court of Appeal reduced by three months the prison term imposed on a Swiss-German fraudster because he was a foreigner. Mr Justice Brian Keith, who delivered that ruling, said that in certain cases a reduction could be made to take into account the extra hardship foreigners faced in Hong Kong jails. The ruling led judges in the lower courts to follow suit. On September 14, Judge Wong extended the principle to mainlanders and reduced the sentences of three defendants.