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As we take a look at who's had the longest wait this month for a family-sponsored immigrant visa, some of these visa categories are on the table in immigration reform talks, with lawmakers proposing to eliminate them.

The idea would be to free up more employment-based visas in a system that has until now favored family sponsorship, and it's drawn backlash from immigrant groups. One proposal being floated is to cut the family categories for married children over 21 and for siblings, who already have a tough time coming to the United States with some of the longest waits.

How long? Here's a look at the the four categories with the longest waits for March, according to the U.S. State Department’s monthly Visa Bulletin:

1) Brothers and sisters of adult U.S. citizens from the Philippines, a wait of more than 23 years (petitions filed July 15, 1989).

2) Married sons and daughters of U.S. citizens from the Philippines, a wait of more than 20 years (petitions filed September 15, 1992)

3) Unmarried adult (21 and over) sons and daughters of U.S. legal permanent residents from Mexico, a wait of more than 20 years (petitions filed January 15, 1993)

4) Married sons and daughters of U.S. citizens from Mexico, a wait of 20 years (petitions filed March 15, 1993)

Visa backlogs and how to deal with them are part of what lawmakers are wrangling with in the immigration reform debate; eliminating family categories was a solution proposed during the last, unsuccessful round of reform negotiations in 2007.

Why this line moves at such a grindingly slow pace for some: The waits are especially long for people who hope to come as immigrants from the Philippines and Mexico — and to a lesser degree from China and India — because there is more demand for family reunification from these countries than available visas will accommodate.

The United States allows every country the same percentage of visas from a pool of family and employer-based visas available each year, regardless of demand from any individual nation. Applicants in countries with high demand are competing for the same number of available visas as people in countries in which there's far less demand. The end result is that they face a much longer wait.

The bulletin displays priority dates going back to when these applicants filed petitions. Having one’s priority date appear in the bulletin is good news, but the dates are subject to change and often do, meaning people who thought their wait was just about over must stay in line longer.

These waits don’t apply to immigrants defined as “immediate” relatives of U.S. citizens, i.e. spouses, parents, and children under 21, all of whom are exempt from the limits (although U.S.-born children of immigrants must be 21 to sponsor parents, and penalties apply if the parents entered illegally).

Read the entire Visa Bulletin for March 2013 here.

Visa All* CHINA** INDIA MEXICO PHILIPPINES F1 Feb. 15, 2006 Feb. 15, 2006 Feb. 15, 2006 July 22, 1993 Oct. 15, 1998 F2A Nov. 22, 2010 Nov. 22, 2010 Nov. 22, 2010 Nov. 15, 2010 Nov. 22, 2010 F2B March 1, 2005 March 1, 2005 March 1, 2005 Jan. 15, 1993 June 8, 2002 F3 July 15, 2002 July 15, 2002 July 15, 2002 March 15, 1993 Sep. 15, 1992 F4 April 22, 2001 April 22, 2001 April 22, 2001 Aug. 15, 1996 July 15, 1989

*All, except those listed.

**Those born in mainland China.