The formula used to calculate the amount of the employer pension contribution is set forth in the October 1, 1996 ILA Master Contract, found at the link below:

Official Website of the ILA: Master Contract & Extension

(The document is not searchable, you will need to proceed page by page to Section #3:CONTRIBUTIONS TO WELFARE, PENSION AND OTHER FRINGE BENEFIT PLANS)

In 2001, the 1996 Master Contract was extended to September 30, 2004. The extension agreement is also available at the link above.