A coalition of leftists and striking teachers blockaded all four major highways to the colonial city of Oaxaca on Friday the latest escalation of a nearly three-month-long protest aimed at ousting the state governor.
A man witnesses described as an angry motorist shot a teacher in the shoulder at a barricade, prompting a scuffle in which several people suffered minor injuries.
The teacher, Benito Castro, was treated at a local hospital for his wound, which did not appear to be life-threatening.
Some demonstrators claimed Oaxaca Gov. Ulises Ruiz was somehow behind the shooting.
They have been demanding his resignation, accusing him using force to repress dissent and of rigging the 2004 election to win office. Ruiz has denied the accusations.
On Friday, motorists sought to enter and leave the city through secondary roads and streets, but traffic was completely choked at points. Some teachers also asked the motorists for donations to support their cause.
The protesters have already seized the city's famous arch-ringed main plaza, state-run media outlets and government buildings, and have forced the cancellation of the state's foremost tourist festival. They have also hijacked city buses and blocked streets in some parts of the city. At other points they have established checkpoints and demanded visitors show identification before being allowed to pass.
The demonstrators recently also blocked the entrances to banks and businesses.
The teachers have said they will not lift their strike, which began on May 22, to allow the state's 1.3 million public school students to begin the school year on Monday.
The 70,000 teachers originally went on strike to demand salary increases totaling about US$125 million (euro97.6 million), but the government said it couldn't afford that and instead offered the teachers less than one-tenth of that amount.
Tourism revenues have suffered in Oaxaca City, a colorful state capital about 520 kilometers (325 miles) southeast of Mexico City that attracts Mexican and foreign tourists.
Negotiations between the state government and protesters have broken down. Oaxacan artist and community leader Francisco Toledo has proposed a civic mediation team, a leader of which would be former Chiapas Bishop Samuel Ruiz, an outspoken advocate of Indian rights and other social causes.