As many as 50 Conservative MPs are threatening to rebel against a government measure due to be debated on Monday that would impose fines on public bodies, including local councils, that seek to mount boycotts against Israel. The proposal – piloted by the communities secretary, Michael Gove – is a Conservative manifesto commitment, and has caused divisions in both main parties, highlighting the controversy surrounding the boycott, divestment and sanctions (BDS) movement. The Tory rebels are likely to abstain on Monday rather than back what they regard as a reasoned Labour amendment, which if agreed would prove fatal to the bill since the measure was in the party election manifesto. A reasoned amendment is a parliamentary procedure by which an MP can object to the provisions of a proposed bill without setting amendments to it. But they will warn ministers that they will have to completely rework the economic activity of public bodies bill or see it rejected outright in later stages of the bill’s passage. The scale of the unease on a foreign policy issue has caught government whips by surprise. Labour said if its reasoned amendment fell at the bill’s second reading on Monday it would abstain. The former shadow chancellor John McDonnell is one of a group of Labour MPs that say they will vote against the bill if the Labour amendment falls. The Labour party after years of difficulties with the Jewish community has undertaken some major outreach to explain why, on the basis of legal advice,it is tabling the reasoned amendment that guts the bill’s enforcement powers. Labour has said the bill has been poorly drafted, might provoke antisemitism and restricts free speech. In an interview with Jewish News, Lisa Nandy, the shadow communities secretary, said: “The bill has been drawn very widely. It gives far-reaching powers to the secretary of state, and has a number of far-reaching implications, none of which appear to have anything to do with tackling BDS, the issue the government says it wants to solve, which we share.” She added: “We also share the concerns raised by MPs of all parties, campaigners and human rights groups that this bill will have a major impact on groups, such as the Uyghur in Xinjiang and other persecuted groups across the world”. The Uyghurs often advocate a boycott of goods coming from Xinjiang on the basis that the goods are products of a form of slave labour. A group of Conservative MPs went to see the government chief whip last week to voice their objections and at the weekend it was thought as many as 50 Tory MPs harbour objections to the measure, including the chair of the foreign affairs select committee, Alicia Kearns. The bill has divided opinion in the Jewish community but has the strong support of the British Board of Deputies, as well as the chair of the Jewish Leadership Council, Keith Black. The Liberal Democrat foreign affairs spokesperson, Layla Moran, said the bill was largely designed to wrongfoot Labour with the Jewish community. Caroline Lucas, the Green MP, said: “It is absolutely appropriate and right for councils and universities to be able to express a view about where they want their money invested, whether they want it invested with companies that commit crimes under international law. That is a basic tenet of our freedom.” The bill seeks to prevent local councils being “influenced by political or moral disapproval of foreign states when taking certain economic decisions”. It also appears to treat the occupied territories, the Golan Heights and Israel as one entity even though the bill also states it does not change UK foreign policy The government also denies that the bill might hinder boycotts of China, saying existing laws already include exceptions to deal with serious issues in supply chains, in line with the procurement bill. These include exceptions for labour market misconduct (including modern slavery), national security, human trafficking, environmental misconduct and bribery.