So what other large entity that opposes same-sex marriage could the mayor take on?

Because they're not discriminatory in their hiring and promoting, nor do they only try to recruit ultra-catholic, married people for employment.

Domino's Pizza, in contrast, seem like it'll hire just about anyone.

:)

The original owner of Domino's is who you're thinking about.

The current owner is a conglomerate of investors led primarily by Bain Capital who bought it from the original owner in 1998 and took the company public in 2004.

So, Domino's got out of the crazy Christian business back in 1998.

A charity is a business that has 501(c)(3) status from the IRS. The IRS's definition is as follows (taken from irs.gov):

To be tax-exempt under section 501(c)(3) of the Internal Revenue Code, an organization must be organized and operated exclusively for exempt purposes set forth in section 501(c)(3), and none of its earnings may inure to any private shareholder or individual. In addition, it may not be an action organization, i.e., it may not attempt to influence legislation as a substantial part of its activities and it may not participate in any campaign activity for or against political candidates.

Organizations described in section 501(c)(3) are commonly referred to as charitable organizations. Organizations described in section 501(c)(3), other than testing for public safety organizations, are eligible to receive tax-deductible contributions in accordance with Code section 170.

Exempt Purposes

The exempt purposes set forth in section 501(c)(3) are charitable, religious, educational, scientific, literary, testing for public safety, fostering national or international amateur sports competition, and preventing cruelty to children or animals. The term charitable is used in its generally accepted legal sense and includes relief of the poor, the distressed, or the underprivileged; advancement of religion; advancement of education or science; erecting or maintaining public buildings, monuments, or works; lessening the burdens of government; lessening neighborhood tensions; eliminating prejudice and discrimination; defending human and civil rights secured by law; and combating community deterioration and juvenile delinquency.

Note: emphasis on "religious" is mine