U.S bishops flatly rejected a plan to rewrite the laws governing legal immigration on Aug. 2, expressing “strong opposition” to a Senate proposal that earlier that day had gained the support of President Trump. Flanked by Republican Senators David Purdue of Georgia and Tom Cotton at Arkansas, President Trump threw his support behind a plan that would end long-standing family reunification policies in favor of a “merit based” system for skilled English speakers. The proposal also includes a substantial cut in the annual numbers of legal immigrants allowed into the United States aimed at reducing legal immigration from the current 1.1 million to about half a million over 10 years.

In a statement issued on behalf of the U.S. Conference of Catholic Bishops, the Most Reverend Joe Vásquez, bishop of Austin and chair of the bishops’ Committee on Migration, urged the Senate to reject the proposed legislation and to instead return to negotiating a comprehensive immigration reform package.

“Had this discriminatory legislation been in place generations ago,” he said, “many of the very people who built and defended this nation would have been excluded.”

President Trump said the measure would “reduce poverty, increase wages and save taxpayers billions and billions of dollars.” He charged that the current system “has not been fair to our people, to our citizens, to our workers.”

But Bishop Vásquez said the act would mean the United States was turning its back on people “setting out to build a better life.”

“As a church,” Bishop Vásquez said, “we believe the stronger the bonds of family, the greater a person’s chance of succeeding in life. The Raise Act imposes a definition of family that would weaken those bonds.” He added that the measure would hinder the nation’s ability to respond to those in crisis.

“The pattern is clear: Deport Latinos, ban Muslims and now this bill would prevent Asians and Africans from entering the country.”

According to the president, the proposal, the first significant rewriting of U.S. immigration policy since the Immigration and Nationality Act of 1965, would favor applicants “who can speak English, financially support themselves and their families and demonstrate skills that will contribute to our economy.” He added that the proposals would prevent new U.S. arrivals from collecting welfare and soon lead to new employment opportunities for unskilled U.S. citizens.

J. Kevin Appleby, the senior director of international migration policy for the Center for Migration Studies and the Scalabrini International Migration Network, was not impressed by the president’s presentation. “It’s all part of their nativist agenda,” he said.

“The pattern is clear: Deport Latinos, ban Muslims and now this bill would prevent Asians and Africans from entering the country.” Mr. Appleby explained that in recent decades, in an attempt to redress past discrimination, immigration numbers from Asia had increased significantly under family reunification policies currently in force, and African green-card holders had benefited most from the diversity visa lottery which each year allocates 50,000 visas to residents of countries that do not currently send a significant number of immigrants to the United States.

“They are trying to create an immigration system in their own image. If you connect the dots they basically want a system that favors those who are more highly skilled and those who are more European,” he said. It is unclear how many Western Europeans with superior English language skills even wish to immigrate to the United States, Mr. Appleby pointed out.

The Reforming American Immigration for Strong Employment, or Raise Act, would end green card preferences for the adult parents, siblings or children of U.S. citizens, retaining preferences for spouses and minor children only. It would also eliminate the diversity lottery and would cap the number of refugees offered permanent residence in the country at 50,000 annually. Refugee quotas are allocated each year but historically have run closer to 70,000 each year and have run as high as 230,000 in recent decades.

“Basically the bill would eviscerate the family-based immigration, which has been the cornerstone of our system for generations and which has served our nation well,” said Mr. Appleby. “Families are economic actors, they strengthen the social cohesion of immigrant communities and protect members from [needing] public assistance.” He added that family connections also act to protect people fleeing persecution in their nations of origin.

“If you couple this with the reduction in the refugee program and [the president’s] stated goals in expanding expedited removal to the whole country, you basically have no U.S. protection regime [for refugees] at all,” Mr. Appleby added.

If part of the plan’s intent were to reduce undocumented migration into the United States, Mr. Appleby is convinced the new proposals would have the opposite effect. The nation’s low unemployment and demand for unskilled labor will only continue to serve as a magnet for migration, he argues. “If you cut legal immigration, people will have no other recourse” but to seek to enter the United States illegally.

“Family reunification has long been a core principal of U.S. immigration policy,” Patricia Zapor, communications director for the Catholic Legal Immigration Network Inc., or CLINIC, told America via email. “Yes, the immigration system needs an overhaul. But it should not be accomplished by sacrificing the basic American and humanitarian principle that families belong together. Families already wait many years to be together under the current system. Making it even harder on families is not who we are as Americans.”

Even with the president’s support, the Raise Act faces a doubtful future in Congress. The proposal has largely been ignored in the Senate since it was introduced in February. Mr. Trump’s backing was meant to give the plan a legislative boost, but so far no other lawmakers in Washington have signed on as co-sponsors and Republican leaders have shown no inclination to vote on immigration this year.

Some immigrant and business advocates have criticized the proposal, saying that slashing legal immigration would hurt industries like agriculture and harm the economy.

“Our system is broken, but the response should be to modernize it, not take a sledgehammer to it,” Jeremy Robbins, executive director of New American Economy, a group of business leaders, mayors and others backed by former New York City Mayor Michael Bloomberg that advocates for comprehensive immigration reform, told the Associated Press.

Mr. Appleby likewise believes the timing of the proposal, from an economic and demographic standpoint, is completely off.

“It’s counter to the trends we’re experiencing,” he said. “We’re at replacement rate now in terms of [native] birth rate; we have an aging population. We are going to see [low-skilled] labor gaps ahead. There will come a point where we will want immigrant workers.

Were the plan implemented, Mr. Appleby foresees a “huge social cost.”

“We have the most diverse and robust economy in the world and and it needs all levels of skills to make it turn,” he said.

And undercutting family reunification policies, he charged, “will lead to another generation of U.S. children being separated from their parents. It attacks the family unit, which is really the glue which holds society together.”

Updated 10:11 a.m. E.D.T., Aug. 3.

Updated at 5:46 p.m. E.D.T. to include a response from the U.S. Conference of Catholic Bishops.

Updated at 3:19 p.m. E.D.T., Aug. 2: Additional reporting from the Associated Press and national correspondent Michael O’Loughlin.

Kevin Clarke is America’s chief correspondent and the author of Oscar Romero: Love Must Win Out (Liturgical Press).