The proposed ban on kosher and halal slaughter in the Netherlands is now highly unlikely to pass into law in a vote due to take place this Tuesday.

The ban, which was backed by the Dutch parliament in June, requires a "yes" vote from a majority in the senate, which devoted a 16-hour debate to the issue this week. But a deal forged between the two biggest parties in the senate, Labour and the Liberals, is almost certain to result in the bill being blocked.

The change of heart emerged during the discussion over the right to freedom of religious practice. A large number of senators agreed that denying that right would be unconstitutional.

During the debate, Nico Schrijver, a Labour senator, revealed that his party had other doubts about the bill, which was originally proposed by the Party for Animals allegedly out of concern for animal rights. Mr Schrijver asked why the bill specifically targeted religious methods as opposed to "large-scale industrial slaughter, which involves 500 million animals per year".

He said he believed there could be "much more effective, and less far-reaching methods that achieve the same goal" of animal welfare.

However, the secretary of Trade and Agriculture, Henk Bleker, did pledge to create a law that will enforce limits on ritual slaughter, such as ensuring that an animal does not suffer for longer than 30 seconds.

The proposed ban, which resulted intense lobbying from the Jewish and Muslim communities, attracted support from a number of groups, including Geert Wilders's Freedom Party, which has a record of being critical of Islam. One Freedom Party senator said at the debate that "such practices" did not belong "in a civilised country as ours".

The bill has been opposed by the Christian Democrats from the outset.

Meanwhile, a group of leading US congressmen and women from both the Republican and Democratic parties this week launched an appeal to the senate to block the legislation.

In a letter to Godefridus de Graaf, the senate president, California Congressman Henry Waxman, New York Congresswoman Carolyn B Maloney and eight others declared that they were "troubled" by the possibility of a prohibition. "A ban on ritual slaughter would unnecessarily restrict the religious freedom of one million Jews and 50,000 Jews in the Netherlands," they said.

They added that it would "unequivocally challenge the democratic principles of religious freedom that both of our nations hold dear". Noting that the US Humane Society considers shechitah to be as humane as other methods, they said banning it would contravene the principles of religious liberty guaranteed by the International Covenant on Civil and Political Rights, to which the Netherlands is a signatory.