At a private meeting on Wednesday afternoon, Florida Sen. Marco Rubio will brief his fellow Republican senators on the details of a comprehensive immigration reform plan set to be released sometime over the next week, and he is expected to assure them that the legislation will contain the "the toughest immigration enforcement laws in U.S. history."

The pitch, however, may be a tough sell for some Republican lawmakers still smarting from past failed attempts to overhaul the nation's immigration system.

Among his colleagues in the Senate Republican caucus, Rubio and the other members of the so-called "Gang of Eight"—the bipartisan group of senators tasked with writing the first draft of a new immigration bill—face many tough critics, particularly Alabama Sen. Jeff Sessions and Iowa Sen. Chuck Grassley, senior Republicans on the Judiciary Committee.

Through press releases, media appearances and official letters sent over the past several weeks, Sessions and Grassley have warned that the immigration bill would not mandate adequate border security and could hurt U.S. workers. They have called for the Gang of Eight, which for months has held weekly meetings behind closed doors, to begin negotiating in public, and they want to see immigration reform done piece-meal, instead of through one giant, comprehensive bill. Last week, Grassley wrote a letter to the Republican members of the Gang of Eight requesting that they brief his staff on the status of the immigration talks no later than Monday, April 8. The meeting never occurred.

With the bill set to be made public in the coming days, skeptical Republican senators will have an opportunity to have some of their questions answered and air their concerns. Many of their questions at the Wednesday meeting, presumably, will concern the immigration enforcement measures in the bill.

So what should lawmakers concerned about enforcement mechanisms expect to hear?

According to an overview of part of the legislation provided to Yahoo News by a source familiar with the bill's language, the enforcement proposals are indeed sweeping: First, the bill would require the federal government to meet specific security and border enforcement goals for 10 years before anyone living in the country illegally is allowed to obtain permanent legal status. (During that ten-year period, they will be allowed to stay in the country through a system of temporary visas.) Applicants who applied for the new, Registered Provisional Immigrant status would be required to continually meet eligibility requirements by remaining employed and in good standing with the law. They also would be required to pay fines, taxes and maintain a physical presence within the United States during the years-long application process.

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If passed, the law ultimately would cost billions of dollars in new spending for border security measures, while creating a visa-exit system to track when people overstay their visa and a program that would enforce workplace compliance laws. There also is language in the bill that would prohibit those currently in the country illegally to receive government-subsidized health insurance benefits tied to the 2010 federal health care law for up to 15 years.

For his part, Rubio should be at ease explaining the bill to his colleagues. Since the overhaul's blueprint was unveiled earlier this year, he has made it his task to sell the bill to skeptical friends on the right who worry that the effort to overhaul immigration laws will amount to nothing more than "amnesty" for illegal immigrants and that the border enforcement rules in the new bill will lack the teeth necessary to prevent future flows of immigrants.

In January, Rubio embarked on a media blitz of conservative radio and television programs in an effort to put Republican minds at ease over the march toward a bill. He tussled with conservative media heavyweights such as Rush Limbaugh, Sean Hannity and Laura Ingraham, who challenged him over parts in the blueprint that offer a path to legality for the nearly 12 million immigrants currently living in the country illegally.

As for the process of passing the bill, Rubio also has vowed to ensure that once the measure's first draft is released to the public, it stays public. There is a fear among Republicans, and even some Democrats, that instead of putting the bill through a process of transparent, regular order, the bill's path toward passage could devolve into the realm of secret, backdoor negotiations that plagued Obamacare in 2009 and 2010.

One of the last things immigration reform advocates want is a sideshow of demonstrators arriving in Washington furious because the final bill is perceived as being the product of crony kickbacks to special interests and backroom dealing. With an issue as emotional and important as immigration, everyone will want to know exactly what's in it long before it's time to take a final vote.

*This article has been updated to reflect that the meeting between Rubio and Senate Republicans was rescheduled to Wednesday.