premise: Two Philippine transport worker groups launched a joint strike here on Monday, protesting against higher gasoline prices.
  In Quezon City, Metro Manila, members of the National Transport Workers Union and the Jeepney Coalition Transport of the Philippines gathered to rally along streets, calling for reduction on pump prices of gasoline, a footage of ABS-CBN TV News Channel showed.
  The groups said that the last two price cuts by the government were negligible. They also called for the scraping of the oil deregulation law, according to the TV report.
  Several public transport routes in Metro Manila were affected, and some school classes have been suspended due to the strike, the metropolitan authorities said.
   Why were some school classes suspended?
hypothesis: due to the strike