For Pedro Hernandez, a striking elementary-school teacher from the southern state of Oaxaca, his union's protests disrupting Mexico's capital aren't just about education. They're about stopping President Enrique Pena Nieto.

"We're against all the structural reforms," the 37-year-old said last week as he walked down Mexico City's central boulevard as part of an organized march of 15,000. Hernandez held a sign that read "Mexico has no president."

The demonstrations, which persuaded Mexican lawmakers to delay votes on education-reform legislation that would have subjected teachers to standardized evaluations, are a sign to Barclays Plc that Pena Nieto may struggle to push through his energy and tax-law plans without modification.