Secondary schools across the country are expected to close today as teachers stage another strike over pay and conditions.

About 20,000 members of the Post Primary Teachers' Association (PPTA) will walk off the job after they 'voted overwhelmingly” to hold the one-day industrial action.

As many as 50,000 teachers and principals staged joint protests across the country on March 16, but today's strike will not include kindergarten and primary staff, who are represented by New Zealand Educational Institute Te Riu Roa.

Some secondary schools will open to supervise younger students, but the exact number is unknown as school boards are not required to inform the Ministry of Education that they intend to close.

Demonstrations are planned in towns and cities across the country, including a protest outside Education Minister Jan Tinetti's office in Greerton, Tauranga, from 10am, organised by members of the Western Bay of Plenty PPTA.

In Auckland, a series of early roadside pickets will be staged outside Green Bay High School, Western Springs College, Selwyn College and Westlake Girls High School.

In the capital, commuters will be met by striking teachers at Johnsonville, Porirua and Wellington train stations, while demonstrations will be held outside MP Greg O'Connor's electorate office in Ohariu and Finance Minister Grant Robertson's office in Willis St.

Unions leaders are trying to finalise multiple collective agreements and Mark Williamson, the ministry's general manager of employment, says they are continuing to negotiate 'in good faith” towards settlements for all teachers and principals.

'Last week was focused on mediated bargaining for the secondary teachers' collective with (the) PPTA,” he says.

'This week is focused on progressing negotiations with the primary sector, with dates in place for the primary teachers and primary principal collective agreements.

'We are also undertaking separate negotiations with the Primary Principals Collective Bargaining Union for primary principals this week.”

NZEI members cannot join Wednesday's strike as they are holding talks with ministry negotiators.

Asked why NZEI members were negotiating on the same day as the PPTA strike, Williamson says: 'We agreed the date of our upcoming bargaining meeting prior to confirmation of PPTA's industrial action.”

PPTA members held the ballot on industrial action last week. As well as Wednesday's strike they voted that from Monday, April 24, (the first day of the next school term) they will not attend meetings outside school hours.

In the second week of next term, PPTA members will put in place a plan to roster different year levels of students home on various days for four weeks.

If the negotiations are not resolved by May they will hold rolling strikes, with teachers striking on different days in different regions.

-Lee Kenny/Stuff.