The trade union Unison has refused the Trade Union Friends of Israel (TUFI) a stall at its annual conference, despite assurances that last year's ban would be lifted.
TUFI, which aims to improve trade union relationships between Israel and Palestine, has run a stall at the conference previously, but last year was refused due to a "security threat" following the Gaza conflict.
After the conference, TUFI was assured it would be considered this year.
Stephen Scott, director of TUFI, said: "We are disappointed that for the second year running we have not been allowed to exhibit.
"We have always striven to put across a moderate trade union case for Israeli unions and their willingness to work with the Palestinian trade unions.
"We are also exhibiting at other unions this year and have had a good reception."
But a Unison spokeswoman said that there was only space at the conference for 20 out of its 80 affiliated organisations.
"We're not affiliated to TUFI, nor are we doing any work with them, so priority goes to those we are currently working with," she said.