(CNN) – The route to legal status for undocumented immigrants, spelled out in pending Senate legislation, could be made even tougher by Congress, Republican Sen. Marco Rubio wrote in an op-ed Friday.
Rubio is one of the most high profile members of a bipartisan "Gang of Eight" senators who unveiled immigration reform legislation last month that includes an eventual pathway to citizenship for many undocumented immigrants. It also mandates tighter border security and better enforcement of current immigration laws.
Some conservatives, including popular radio talk show hosts, have said the pathway amounts to amnesty, and have lambasted Rubio for his role in the bill.
"I've been listening to the voices on these platforms and taking notes about ways to improve the immigration-reform legislation," Rubio wrote in the Wall Street Journal, saying he's heard concerns the border security "triggers" included in the bill aren't stringent enough, and that implementing the new law would be costly.
The bulk of public outcry, however, has remained on the pathway to citizenship. In the proposed legislation, it would take 10 years for the majority of undocumented immigrants to get green cards and then another three years to gain citizenship.
The process would also be contingent on bolstering security. The legislation mandates strict new controls on the U.S.-Mexico border before any pathway to legality is opened. Yet some critics have wondered how the federal government will enforce tighter border security in the future if it has failed to apply current laws up until now.
"For those who have suggested that the border security triggers outlined in the Senate bill aren't strong enough, we now have a chance to strengthen them," Rubio wrote, noting that concerns the pathway is "too generous or lenient" would also be addressed.
"Congress will have a chance to make it tougher, yet still realistic," he wrote. "No one has a right to violate the immigration laws and remain here with impunity. Finding a sensible way to resolve our illegal-immigration problem must include penalties that show the rest of the world that it really is cheaper, easier and faster to immigrate to the U.S. the right way."
Rubio, elected to the Senate in 2010 with strong support from tea party activists and other grassroots conservatives, is thought to be mulling a possible bid for the 2016 GOP nomination, and pundits question whether his push for immigration reform will hurt or help any potential White House run.
On Thursday, the conservative magazine National Review unveiled its May cover: a photo of Rubio unveiling the Senate immigration legislation with the headline "Rubio's Folly."
The senator's op-ed Friday was the latest stop on Rubio's tour to allay the fears of conservatives on immigration. He's made the rounds of right-wing radio talk shows, including on Monday, when he told host Mike Gallagher the current version of the bill was unlikely to gain enough support for approval in the GOP-led House of Representatives.
"It will have to be adjusted, because people are very suspicious about the willingness of the government to enforce the laws now," Rubio said.
That suspicion, and the ensuing suggestions on how to improve the bill, are an important part of the political process, Rubio wrote Friday.
"The immigration-reform bill in the Senate is a solid starting point for solving this problem, and I believe it can be made even better as Congress begins to actively work on it in committee next week," he wrote. "But defeating it without offering an alternative cannot be the conservative position on immigration reform."
CNN's Ashley Killough contributed to this report.