The law doesn't mention font scaling specifically, but as it was clearly
designed for people with poor eyesight, it isn't a big leap.
SEC. 508. ELECTRONIC AND INFORMATION TECHNOLOGY
(a) REQUIREMENTS FOR FEDERAL DEPARTMENTS AND AGENCIES.--
(1) ACCESSIBILITY.--
(A) DEVELOPMENT, PROCUREMENT, MAINTENANCE, OR USE OF ELECTRONIC AND
INFORMATION TECHNOLOGY.--When developing, procuring, maintaining, or using
electronic and information technology, each Federal department or agency,
including the United States Postal Service, shall ensure, unless an undue
burden would be imposed on the department or agency, that the electronic and
information technology allows, regardless of the type of medium of the
technology--
(i) individuals with disabilities who are Federal employees to have access
to and use of information and data that is comparable to the access to and
use of the information and data by Federal employees who are not individuals
with disabilities; and
(ii) individuals with disabilities who are members of the public seeking
information or services from a Federal department or agency to have access
to and use of information and data that is comparable to the access to and
use of the information and data by such members of the public who are not
individuals with disabilities.
http://www.section508.gov/index.cfm?FuseAction=Content&ID=14