We recommend using wording like this:
My institution, the University of Maryland, Baltimore County, requires that I provide immediate open access to my work, {title} to be published in {journal}. Does your author agreement allow for this? If not, would you consider adding the attached addendum to my author agreement?
ADDENDUM
If the response is negative, use the Waiver form to exempt the work from the policy. The exemption is automatically granted upon submission of the form.