EU and U.S. negotiators met at the European Commission in Brussels on Monday to mark the start of a 12th round of negotiations for a free trade deal between Europe and the United States amid a bout of protests.
Wearing helmets and reflective clothes, Greenpeace activists earlier attempted to block access to the meeting in the Belgian capital.
Activists hung banners reading "TTIP: Dead End Trade Deal" on the building's facade and blocked its main gates with wooden panels.
Negotiators managed to enter the building but only after Belgian police asked Greenpeace to keep at least one access to the building free.
The new round of negotiations will last a week and be between the 28-member bloc and the U.S.
The previous round of discussions on a Transatlantic Trade and Investment Partnership (TTIP) was held in Miami, Florida between Oct.19-23, 2015.
Businesses hope the trade pact will deliver over $100 billion of economic gains on both sides of the Atlantic.
Opponents fear TTIP will erode democracy, as well as European health, consumer safety and environmental standards.
The U.S. and the European Union expect to reach a final agreement by the end of 2016.