The so called Reagan amnesty took 5 years and an act of congess to be put into law.
It was also a bipartisian act of congress.

bold emphasis mine

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Statement on Signing the Immigration Reform and Control Act of 1986

 http://www.reagan.utexas.edu/archives/
speeches/1986/110686b.htm
excerpts:
In 1981 this administration asked the Congress to pass a comprehensive legislative package, including employer sanctions, other measures to increase enforcement of the immigration laws, and legalization.

New INA section 245A(d)(2) states that no alien would qualify for the lawful temporary or permanent residence status provided in that section if ``likely to become [a] public charge [ ].'' This disqualification could be waived by the Attorney General under certain circumstances. A likelihood that an applicant would become a public charge would exist, for example, if the applicant had failed to demonstrate either a history of employment in the United States of a kind that would provide sufficient means without public cash assistance for the support of the alien and his likely dependents who are not United States citizens or the possession of independent means sufficient by itself for such support for an indefinite period.

Also known as the Simpson-Mazzoli Act
http://en.wikipedia.org/wiki/Immigration_Reform
_and_Control_Act_of_1986
excerpt:
Romano L. Mazzoli was a Democratic representative from Kentucky and Alan K. Simpson was a Republican senator from Wyoming who chaired their respective immigration subcommittees in Congress. Their effort was assisted by the recommendations of the bipartisan Commission on Immigration Reform, chaired by Rev. Theodore Hesburgh, then President of the University of Notre Dame.

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More reading here

http://wafflesatnoon.com/2008/07/20/the-immigration
-reform-act-of-1986/
excerpt:
This was my final term paper for a Political Science class in college, dated March 6, 1989

excerpt:
President Reagan, though not a key player in the bill, was the catalyst for action by making several proposals to Congress in 1981 on ways to fight the rising number of illegal aliens coming to the United States.