Fast-food giant McDonald's has come under attack from unions for beefing up the price of its hamburgers in Hong Kong while paying its part-time staff less than the average market wage. The average 4 per cent price rise, effective since just before Christmas, followed the chain's first quarterly loss in 47 years because of fierce competition from rivals such as Burger King. But a simple hamburger at Hong Kong McDonald's has almost doubled in price - from $3 to $5.50. In contrast, McDonald's in Japan has cut its prices to 80 yen ($5.20) for a hamburger. According to a survey by the Federation of Trade Unions on the hourly pay for part-time workers at 11 chain stores - including McDonald's, ParknShop, Wellcome, 7-Eleven and Maxim's - McDonald's pays its staff the lowest wages. Part-time workers at McDonald's are paid an average of $15.40 an hour, compared with $22.50 at 7-Eleven, $21.40 at ParknShop, $20.50 at Maxim's and $20.40 at Wellcome. The federation's organising secretary, Chan King-chi, said: 'McDonald's has no grounds to raise its prices when the economy is so bad. It would be reasonable only if they increase the wages for the low-rank employees. 'McDonald's in Hong Kong is the most profitable but pays less than the average for its part-time workers.' McDonald's declined to say if the extra money generated from the price rises would benefit its part-time workers. It also refused to disclose the hourly rate or the number of part-time workers it employed, saying only that its full-time staff of about 11,000 had enjoyed an accumulated pay rise of 6 per cent since 1998. 'In the free market economy that Hong Kong is, we have to be competitive with our wages in order to employ the more than 10,000 restaurant employees that serve our customers all year round,' a company statement said. A spokesman for McDonald's added: 'We haven't raised the price of everything. The adjustment is needed and we have not laid off any staff. 'It is difficult to give a comparison of the prices in different countries. 'Hong Kong is still one of the most inexpensive [McDonald's] in the world.' The director of Lingnan University's Centre for Public Policy Studies, Professor Ho Lok-sang, said: 'It did surprise me that McDonald's raised its prices at a time when consuming power is so weak. 'It's a bit weird that they are increasing the prices without offering more value-added services. 'The public will tell them whether they think it's too expensive.' At least one family will be shunning McDonald's after the price rise. Six-year-old Lau Wai-kin used to have his monthly treat of a hamburger at McDonald's when it cost just $3 - but not any more. 'It's getting too expensive,' said his mother, Hip Oi-yee, 35, who is widowed and lives on social welfare. 'I don't know when we can go back again.' The restaurant chain has more than 200 outlets in Hong Kong. It last raised prices on July 1, 2001. Dr Edwin Lai Lun-cheung, associate professor at City University's Department of Economics and Finance, said McDonald's might be able to increase profits because of the price rises, even though it may drive away some customers. 'If it requires less skill to work at McDonald's than other fast food joints, it may be able to offer lower wages,' he said.