Sen. Marco Rubio (R-Fla.) wants to strengthen requirements in a sweeping immigration bill that mandate that illegal immigrants learn English before earning permanent U.S. residency.

WASHINGTON, DC - MARCH 13: Immigrant families, some of who participated in a 3-week bus tour aimed at keeping families together, came to Captiol Hill on Wednesday demanding legislation with a path to citizenship. A large group went to the office of Senator Marco Rubio, to demand that the senator play an active role in passing immigration reform. Many immigrants spoke about their situations to a staff member. Jesus Guevara Roque, 40, right of Florida is on the left, and Rosmery Martell, 26, of DC is on the right holding her 3 month-old daughter Angie Martinez. Both of them are undocumented. (Photo by Sarah L. Voisin/The Washington Post) Immigrant families visited the Captiol Hill office of Sen. Marco Rubio  in March to demand legislation with a path to citizenship. (Sarah L. Voisin/The Washington Post)

Under the current bill, immigrants would have to earn English proficiency or show they are enrolled in a language course. Rubio, a member of the bipartisan group that developed the legislation, plans to offer an amendment that would eliminate the second provision and require that undocumented immigrants be able to read, write and speak English before earning a green card.

The Senate bill allows undocumented immigrants to apply for a green card after 10 years and then apply for citizenship three years later.

“On the day we announced the principles that would shape the immigration bill, we made it clear that English proficiency would now be required for permanent residency for the first time in American history,” Rubio said in a statement. “This amendment ensures that will be the case."

Rubio is considered a key member of the bipartisan group because of his appeal to conservatives, but he has said recently that the legislation will not earn enough Republican support without changes to strengthen border security.

That has left Democrats and immigration advocates fearful that opponents will lard the bill with too many roadblocks for immigrants to earn citizenship.

“Since the bill was introduced two months ago, the open and transparent process it has undergone has elicited constructive criticisms to improve it,” Rubio said. “This is one of the bill’s shortcomings that came to light, which we can now fix.”

The Senate is expected to vote Tuesday on a motion to proceed with the immigration bill, and members on both sides of the aisle are developing a lengthy list of amendments. Senate leaders have said they hope to hold a vote on the bill before July 4.