Sen. Dianne Feinstein, D-Calif., told then-President Barack Obama in the summer of 2014 that he could use "very broad power" to limit immigration as he saw fit, according to a letter obtained by Fox News.

In the July 29 letter, Feinstein cites Section 212(f) of the Immigration and Nationality Act -- the same federal legislation cited by the Trump administration Thursday in unveiling a rule denying asylum claims to migrants who enter the country illegally.

"Whenever the president finds that the entry of any aliens or of any class of aliens into the United States would be detrimental to the interests of the United States," the legislation states, "he may by proclamation, and for such period as he shall deem necessary, suspend the entry of all aliens or any class of aliens as immigrants or nonimmigrants, or impose on the entry of aliens any restrictions he may deem to be appropriate."

Feinstein's letter initially notes that the senator has discussed possible legislation with then-Homeland Security Secretary Jeh Johnson. Feinstein then writes: "there is also an argument that there is sufficient flexibility in current law for the government to respond to the current crisis and that further legislation is not needed." She adds that the authority vested in the presidency by Section 212 (f) means that "no legislation is necessary to give your administration the tools it needs to respond to this crisis, and that any needed temporary measures can be implemented through presidential action."

In response to Feinstein, then-acting Immigration and Customs Enforcement Director Thomas Winkowski wrote that "[w]hile there is no express prohibition on using the broad, general authority conferred by section 212(f) to help respond to the influx of unaccompanied children, any such use would require careful study ..."

Representatives for Feinstein did not immediately return emailed requests for comment. Since Trump's election, Feinstein has been a prominent critic of his immigration policy.

"There is an unprecedented crisis at our Southern border where aliens understand that they can enter the country illegally, avoid removal, and ultimately remain in the U.S. living and working illegally," U.S. Citizenship and Immigration Services spokesman Michael Bars said in a statement. "The congressionally delegated authority for our president to handle crises at our border appropriately is recognized historically as a bipartisan approach to solving some of the most endemic challenges to national security and public safety. By strengthening the integrity of our lawful immigration system, both the interests of the American people and legitimate asylum seekers properly presenting themselves at ports of entry prevail."