By the 31 December 1998 deadline for firms to sign up to pay to remain on the register under the public-private system, fewer than 6000 firms had rejoined.
Constructionline said it expects to increase its members to more than 6000 by the end of February after a further effort to persuade companies to pay.
It said that it always expected to lose thousands of firms because of the new charging regime. It will now write to 3000 previously unregistered firms to ask them to sign up.
Constructionline has been dogged by controversy since its launch last July, with contractors complaining that its terms – since revised – were too onerous. But it received a boost this week with messages of support from the National Federation of Builders and the Housing Corporation.