* EU investigation into Chinese exports of solar panels
* Alleged dumping of and subsidies for Chinese panels
* Registration would allow back-dating of duties, if set (Adds reaction from pro- and anti-duty groups)
BRUSSELS, March 5 (Reuters) - European Union duties on solar panels coming from China could take effect retroactively from this month after the European Commission ordered EU customs officials to start registering imports of them from Wednesday.
The European Commission last September launched an investigation into whether Chinese solar panels were being dumped in EU markets and in November began a study into allegations of illegal subsidies.
The Commission has until June 6 to impose provisional duties on the imports if it believes they are justified. The deadline for imposing definitive duties, which would require a vote by member states, is Dec. 5.
With the registration of imports, dumping duties could be back-dated to March 6, however.
With Chinese solar panel exports to the EU of 21 billion euros ($27.3 billion) in 2011, the investigation is by far the largest the Commission has ever launched.
The EU ProSun group of 25 solar panel producers, which wants duties, and the association of importers and installers, AFASE, which opposes them, agreed on one thing - registration would have an immediate impact on the market.
The risk that duties could eventually be imposed would make importers hesitant, they said.
EU ProSun, whose complaint prompted the investigation, said Chinese importers had stockpiled supplies in recent months. When the United States carried out a similar action last year, Chinese supply there fell 80 percent, the group said.
AFASE said registration was totally unwarranted and against EU law, which states that duties can be applied retroactively only when imports are rising sharply. It said they were not.
The Commission said the registration procedure relates to imports of solar panels, cells and wafers originating from or shipped from China, according to a regulation published on Tuesday in the EU’s Official Journal.
Chinese producers include Yingli Green Energy, Suntech Power Holdings Co Ltd and Trina Solar Ltd
AFASE last week released a report saying the imposition of duties could cost up to 242,000 jobs.
At a news conference on Tuesday, EU ProSun, which is led by Germany’s Solarworld, sought to pull apart the findings of that report, saying it did not take into account imports from other countries such as Korea and technological advances that would cut prices further.
It also said the sector employed a total of 265,000 people in the EU and that AFASE’s job loss estimate was inconceivable. ($1 = 0.7687 euros) (Reporting By Philip Blenkinsop; editing by Jane Baird)