(CNN) -- The border with Mexico must be secure.
This requirement is the cornerstone of an immigration reform bill a bipartisan group of senators are to file on Capitol Hill on Tuesday. There will be no path to legal residency for migrants without it.
Undocumented immigrants may also not reach the status of fully legal residents under the proposed legislation, until the Department of Homeland Security has implemented measures to prevent "unauthorized workers from obtaining employment in the United States."
The bill drafted by the "Gang of Eight" senators stipulates that the security of "high risk border sectors along the Southern border" must be verified, before most undocumented immigrants can access pathways to legal residency laid out in the proposed legislation.
The bill makes exceptions for those eligible for the DREAM Act, law-abiding immigrants who arrived in the United States as minors and then went on to completed high school. It also includes allowances for certain agricultural laborers.
Conservative senators have insisted upon the border preconditions, and some Democrats have agreed to it. The latter party holds the majority of seats in the Senate.
Once border security has been established via criteria laid out in the legislation, many undocumented migrants would get a shot at gaining legal footing in the United States, according to a summary of the proposed legislation passed on to CNN.
But it will take time to establish border security and the pathway to residency can be costly and take more than a decade to complete, although it is quick to reward successful applicants with the right to participate freely in America's workforce.
Quota-based border security
The bipartisan bill lays down strict criteria for the creation of a secure border.
It calls for $3 billion to beef up border security, which includes fortifying fences, staffing up patrols and acquiring surveillance technology from the Department of Defense, including drones and drone pilots.
Border officers must keep "High Risk Sectors along the Southern Border" under constant surveillance, and they must apprehend and turn back at least 90% of those who cross into the United States illegally each year.
A high-risk border sector is defined as a section where the number of apprehended illegal crossers tops 30,000 per year, according to the summary.
The achievement of border security is based on maintaining that quota.
"If an Effectiveness Rate of 90% or higher for all High Risk border sectors is reached during the first five years after the bill is enacted -- the 'Border Security Goal' has been achieved," the summary reads.
The path to legal residency? Border security
The bill summary introduces two statuses on the pathway to legal residency: registered provisional immigrant (RPI) and lawful permanent resident. Neither is attainable without border security, with the exception of immigrants eligible for the DREAM Act.
To be considered eligible, an undocumented immigrant cannot have arrived in the United States after December 31, 2011, and cannot have any felony convictions in the United States or abroad.
But smaller offenses can also block residency. For example, the applicant cannot accumulate three misdemeanor convictions, such as reckless driving, trespassing or vandalism. Voting illegally also triggers ineligibility and authorities can turn back applicants if they have certain infectious diseases or questionable "morality."
Time and money
Legal status can also be pricey. An undocumented immigrant must pay a penalty of up to $500 for having come to the United States illegally and also pay any owed back taxes as part of attaining provisional consideration.
But once the applicant qualifies for that status, the registered provisional immigrant may work for any U.S. employer and is free to travel outside the country.
The status lasts for six years and can be extended for an additional $500 fee, if the applicant has not gotten into any trouble with the law.
After 10 years as provisional, an immigrant may become a lawful permanent resident by following the same guidelines other immigrants must use to receive a green card, which includes a fee of $1,000.
Again, before any provisional status RPI is allowed to transition into lawful permanent resident status, the Southern border must be certifiably secure.
In addition, the secretary of Homeland Security must have "implemented a mandatory employment verification system to be used by all employers to prevent unauthorized workers from obtaining employment in the United States," according to the bill summary.
Meeting with Obama
Two senators from the "Gang of Eight" -- John McCain, R-Arizona, and Chuck Schumer, D-New York -- discussed the bill with President Barack Obama on Tuesday at the White House.
Out of respect for the victims of the violence that marred the marathon, Schumer and McCain canceled a news conference on Tuesday where the proposal was to have been formally rolled out.
The other legislators in the "Gang of Eight" are Sen. Michael Bennet, D-Colorado; Sen. Marco Rubio, R-Florida; Sen. Lindsey Graham, R-South Carolina; Sen. Jeff Flake, R-Arizona; Sen. Robert Menendez, D-New Jersey; and Sen. Dick Durbin, D-Illinois.
Members of the Republican-led House of Representatives, which is typically more conservative than the Senate, are working on their own immigration overhaul plan, which also includes border security measures.
Blue card for ag workers
The "Gang of Eight" proposal calls for issuing agricultural workers a new type of legal status card: a blue card.
Agricultural workers who are currently in the country illegally can apply for the card if they have worked in the U.S. agriculture industry for at least 100 days in the two years prior to Dec. 31, 2012.
Applicants must also pay a $400 fee, show they have paid their taxes and have not committed a criminal offense.
The bill sets caps for new guest agricultural workers. Just over 112,333 cards would be issued per year for the first five years.
And depending on the type of work they are doing, some agricultural workers in the country illegally will have to continue to work a certain period of time in that industry in order to stay in the country.
Agricultural workers under the program would be eligible for a green card in five years, half the time of other adult immigrants in the country illegally, according to the legislation.
The proposal would also set minimum wages across several categories of agricultural workers.