The UN human rights commissioner, Zeid Ra’ad al-Hussein, has sent letters to an estimated 150 international and Israeli businesses warning them that they may be included in a UN database of companies involved with illegal Jewish settlements in the occupied Palestinian territories.

The letters have been sent as part of the legal verification and clarification process to give businesses identified as working in settlements the right of reply before the database is published in December.

Reports that the high commissioner’s office was pushing ahead with its work to publish the database by the end of this year, despite the strong opposition of the Trump administration and Israel, emerged in August.

It gained new impetus with a claim in the Israeli newspaper Haaretz that about 150 letters had been sent in the past fortnight, including a number that had been passed on to Israeli officials.

An anonymous Israeli official quoted by the paper said these firms had been told in the letter that they had been identified as doing business in the “occupied Palestinian territories” and could thus be acting in violation of “internal law and UN decisions”.

The most recent UN resolution on the 50-year Israeli occupation – resolution 2,334, which was adopted by the security council in 2016 – described Israeli settlement activity in the occupied territories as having “no legal validity and constitut[ing] a flagrant violation under international law”.

According to the report of the companies to receive letters so far, the largest number of foreign organisations were US concerns – about 30 – while half were Israeli.

While an official in the office of the Israeli prime minister, Benjamin Netanyahu, declined to comment, Palestinian officials told the Guardian they understood that work on the database was moving forward and that the letters were part of the formal notification process.

While the database – whose creation was mandated last year – has no legally binding standing in its own right, there is evidence that foreign businesses in particular are becoming increasingly concerned over the potential for future legal challenges over doing business in the occupied territories as well as adverse publicity and shareholder activism from groups such as church pension funds.

Hussein, a former Jordanian diplomat in whose name the letters has reportedly been sent out, has indicated to diplomats that he intends to publish the list by the end of the year. He has also asked for comments from countries where affected firms are headquartered.

Last month, a US state department official said the Trump administration would not cooperate with the creation of the database. “We have made clear our opposition regarding the creation of a database of businesses operating in Israeli settlements in the occupied territories, and we have not participated and will not participate in its creation or contribute to its content,” she said.

For her part, the strongly pro-Israel US ambassador to the UN, Nikki Haley, has described the list as “shameful”, while her Israeli counterpart denounced the database as a modern form of antisemitism.