Disclaimer. Don't rely on these old notes in lieu of reading the literature, but they can jog your memory. As a grad student long ago, my peers and I collaborated to write and exchange summaries of political science research. I posted them to a wiki-style website. "Wikisum" is now dead but archived here. I cannot vouch for these notes' accuracy, nor can I say who wrote them.
Nacif. 2002. Understanding party discipline in the Mexican Chamber of Deputies: The centralized party model. In Legislative Politics in latin American, eds. Nacif and Morgenstern.
Why is party discipline so high in the Mexican chamber of deputies?
MAIN ARGUMENT: The high level of party discipline in the Mexican Chamber of Deputies is explained by the control of nominations to legislative office by party leaders and one institutional feature of the Mexican political system: legislators cannot run for reelections in consecutive terms.
Consequence: Candidate in single-member districts depend on the decisions made by the electorate, whereas candidates in multimember districts depend on party leadership, particularly the National Executive Committee of the party. The power of the National Executive Committee (CEN) is reinforced by the fact that the PR seats operate under closed lists and the fact that independent candidates are prohibited. The higher a politician is on the list the more possibilities he has to become in office.
Legislators advance via promotion (by the party) more than via election. Therefore, ambitious candidates do well if they serve the party reliably and skillfullly. Unlike US candidates (who must maintain ties to constituencies), Mexican deputies must maintain ties to the party. Even though there may be factions within a legislative party, your first loyalty must lie with the party leadership.
Research on similar subjects