ST. PAUL, MINN. — The black mayor of St. Paul, Minnesota, has received racist threats amid a long-simmering dispute over how the city should collect its trash.

Police in Minnesota's capital are investigating threatening and racist messages to Mayor Melvin Carter in the run-up to a citywide vote on organized trash collection.

A St. Paul police spokesman says an anonymous caller using racial slurs left a voicemail at Carter's office on Monday. The caller warned that if taxes increase, Carter will have to "pay for it" and be forced to put "bulletproof windows" in his house. Carter also received racist hate mail earlier this month.

Carter is St. Paul's first African American mayor. The mayor's office says it takes all threats seriously.

Carter has warned that the city could face hefty property tax hikes if voters reject the trash ordinance on Nov. 5.