Accessory maker Hebie of Germany has also joined ETRA this week.
ETRA is active as a bicycle trade lobbyist in Brussel.
Annick Roetynck, secretary of ETRA, said: "With their membership both Giant and Hebie underline the importance they attach to a strong dealer network for the marketing and the distribution of their products. Moreover, they subscribe to the viewpoint that in order to grow the market cycle usage needs to be promoted."
Tony Lo, president of the Giant Group, said: We have always been impressed by the good work ETRA has done on behalf of two-wheel retailers and for cycling advocacy in Europe. We consider ourselves a retail supporting company, we are eager to do things to help retailers become more successful.
ETRA believes that the time for political pressure on the European Commission, Parliament and Council to promote cycling has never been better.
"Lobbying should be intensified on issues such as infrastructure, road safety, taxation, and product quality," said Roetynck.
"The energy crisis, transport, environmental and health issues are hitting the media headlines almost every day. The media pressure goes together with a growing public awareness. ETRA believes this will lead to actions by the European authorities. ETRA wishes to be fighting for and on behalf of the cycling community to influence the decisions that will be made in that framework."
ETRA wants more associate members to join from the bike trade. Existing members include Shimano and Bohle.