Exploitation of Employers

Workers Will Be on the Move in the New Year
"The new year is expected to usher in a flurry of job hopping as employees frustrated by years of incremental raises and scarce advancement opportunities begin shopping for new employers.

Nearly half of U.S. companies face an employee exodus as the economy improves, according to a survey by Novations Selection, Development and Communication, a performance improvement firm. Typically, fewer than 10% of employers would expect such turnover."
(USA Today, Monday)

Who will defend employers against this exploitation by workers?

When employers seek to reduce costs and increase profits by shopping for lower-cost labor, this is called exploitation. Labor unions are formed to protect workers from such 'exploitation' by making it much more difficult for employers to fire employees, which naturally results in lowered standards of performance. When employees seek to increase profits by shopping for higher-paying jobs, is this therefore also exploitation?