"It is not just a matter of proper policy and humanity, but also Denmark's international reputation," a group of ten local and regional Venstre politicians wrote in the Berlingske daily.
"When focusing on symbolic actions rather than real content, you forget that politics is about real people of flesh and blood," they said.
Denmark already had laws that could be used to require wealthy migrants to support themselves, they argued.
"What is new is... expanded powers to search refugees' luggage for money and valuables," they said.
The bill looks set to pass in parliament on January 26 after the government on Tuesday secured a parliamentary majority. A series of debates will begin on Wednesday.
A European lawmaker for Venstre last month left the party over its ever tighter migration policies, which have included delaying family reunification times and advertising in Lebanese newspapers to deter refugees from coming to Denmark.
But observers believe the party's leadership is unlikely to be influenced by critics of Integration Minister Inger Støjberg's hardline policies.
"There is complete and totally unequivocal backing for Inger Støjberg's course. Prime Minister Lars Løkke Rasmussen has chosen her himself, and he knows what he has chosen," Troels Mylenberg, the editor of regional daily Fyns Amts Avis, told news agency Ritzau.
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Copenhagen's minority government and its right-wing allies -- the far-right Danish People's Party, the Liberal Alliance and the Conservative People's Party -- reached an agreement on the bill on Tuesday with the opposition Social Democrats, meaning it is now supported by a majority of parties in parliament.
The amended bill would allow Danish authorities to seize migrants' cash exceeding 10,000 kroner (1,340 euros, $1,450), as well as any individual items valued at more than 10,000 kroner.
Wedding rings and other items of sentimental value would be exempt, the agreement said, also citing engagement rings, family portraits and medals.