FRANKFURT, July 13 (Reuters) - The world's four biggest automotive industry associations have written to China's government to demand it change its plans for strict sales quotas for electrically powered vehicles, German weekly magazine WirtschaftsWoche reported, citing the letter.

The associations, based in Europe, the United States, Japan and South Korea and representing around 70 percent of global car production, also called for the quotas to be postponed by at least one to three years, the magazine said on Thursday.

China last month upheld the sales quotas for electric cars in draft regulation, ignoring concessions that had been agreed between Chinese Premier Li Keqiang and German Chancellor Angela Merkel.

The draft says that automakers must sell enough electric or plug-in hybrid vehicles to generate "credits" equivalent to 8 percent of sales by 2018, 10 percent by 2019 and 12 percent by 2020 -- criteria many in the industry deem too ambitious.

The number of credits per car is based on the level of electrification.

According to WirtschaftsWoche, the industry associations are demanding that the Chinese government includes less harsh penalties for failing to reach the sales quota, and that it tailors the quota to each carmaker's production volume to avoid putting companies that make a smaller number of vehicles at a disadvantage. (Reporting by Maria Sheahan; Editing by Keith Weir)