From the Orlando Sentinel:

U.S. Sen. Mel Martinez will endorse Republican presidential candidate John McCain later today, according to a person close to McCain's campaign.

Martinez will announce the endorsement at an event in Miami, the person said.

A former Orange County mayor, Martinez is popular with Cuban-American voters who are a crucial voting bloc in Florida GOP elections.

UPDATE: A second source close to the campaign confirmed the news. The endorsement is expected to come at a meeting of the Latin Builders Association, which McCain is scheduled to address at 4:45 p.m.