A proposal to reduce Davis Cup singles matches to the best-of-three sets has been rejected - but could still be implemented on a trial basis in 2018.
The proposal fell short as it was was backed by 63.54% of voters at the AGM, with a two-thirds majority required.
ITF president David Haggerty said the vote result was "disappointing".
However, a later resolution gave the ITF board the power to make changes on a trial basis from 2018 without wider approval from the general membership.
"This is a ground-breaking decision," added Haggerty.
"The resolution gives the board the latitude and flexibility of trialling changes to Davis Cup and Fed Cup without waiting for approval of the AGM.
"In a fast-changing world, we need to be agile and nimble to make decisions, and this resolution gives us that ability."
World number one Andy Murray has called for Davis Cup matches to be shortened to increase the participation of top players.
A motion was approved guaranteeing both the Davis Cup and women's Fed Cup finalists the choice of hosting their first-round ties the following year.