The law, enacted this year, requires at least 75 percent of voting machines to be used in each election, said Secretary of State Delbert Hosemann.
Previous state law didn't specify what percentage of machines must be used in elections. During the 2010 congressional races, some counties put out too few machines, and voters in several precincts encountered long lines, Hosemann said. The new law came in response to that situation.
"Hopefully, the lines will be shorter and you'll have less time at the voting booth so you can come and go quickly," Hosemann told The Associated Press on Monday.
Polls will be open 7 a.m.-7 p.m. Tuesday as Mississippi holds Democratic and Republican primaries for statewide, regional, legislative and county offices.
Democrats' only statewide contested primary is for governor. Republicans have contested statewide primaries for governor, lieutenant governor, treasurer, agriculture commissioner and secretary of state.
Runoffs, if necessary, will be Aug. 23. The general election is Nov. 8.
The U.S. Justice Department said it will monitor the primaries in 11 of Mississippi's 82 counties to ensure black voters' rights are protected. Federal observers will be in Bolivar, Clay, Copiah, Humphreys, Jefferson Davis, Noxubee, Panola, Quitman, Sunflower, Tallahatchie and Wilkinson counties. Ten of the 11 counties are majority black. Only Panola is not.
Hosemann said the secretary of state's staff on Tuesday will be in more than 30 counties to check on several operational questions, including whether precincts open on time, disabled voters have access to ballots and contested ballots are handled properly.
Hosemann said Monday he would not predict the level of voter turnout for the primaries, which are conducted by the Democratic and Republican parties.
Republican Gov. Haley Barbour is limited to two terms and couldn't run this year.
The four candidates in the Democratic primary for governor are Hattiesburg Mayor Johnny DuPree, Clarksdale attorney and businessman Bill Luckett, Meridian High School history teacher William Bond Compton Jr. and retired Yalobusha County tax assessor Guy Dale Shaw of Coffeeville.
The five candidates in the Republican primary for governor are Lt. Gov. Phil Bryant of Brandon, construction executive Dave Dennis of Pass Christian, businessman Ron Williams of Moss Point, Pearl River County supervisor Hudson Holliday of Poplarville and former state employee James Broadwater of Byram.
The Democratic and Republican nominees for governor will face independent Will Oatis of Silver Creek in the general election. Two rival Reform Party groups want to put a candidate in the governor's race. After the major parties' primaries are completed, the state Elections Commission could consider which Reform slate will be on the November ballot. The Reform Party has no history of winning statewide elections in Mississippi.
One of the biggest draws on the Republican side Tuesday could be the lieutenant governor's primary between state Sen. Billy Hewes of Gulfport and state Treasurer Tate Reeves of Flowood. The winner likely will hold the office for the four-year term that begins in January, because no Democrat is running. The feuding Reform Party factions also want to put a candidate on the general election ballot for lieutenant governor.
Candidates in the Republican primary for treasurer are state Personnel Board director Lynn Fitch of Madison, attorney and former Barbour budget adviser Lucien Smith of Jackson, and state Sen. Lee Yancey of Brandon. In the general election, the GOP nominee will face Democrat Connie Moran, who is mayor of Ocean Springs, and a Reform Party candidate.
The current agriculture commissioner, Republican Lester Spell, did not seek a fifth term this year. Candidates in the Republican primary are state Sen. Cindy Hyde-Smith of Brookhaven, retired agriculture educator Max Phillips of Taylorsville and state Rep. Dannie Reed of Ackerman. The Republican nominee will face Democrat Joel Gill of Pickens, a cattleman, in the general election.
Candidates in the Republican primary for secretary of state are Hosemann, the first-term incumbent from Jackson; and Ricky Dombrowski, a member of the Gulfport City Council. No Democrat is running for secretary of state, but a Reform Party candidate will be on the November ballot.