Scottish Labour MSPs will only cross picket lines of striking workers at Holyrood this week on “urgent or serious” matters with the permission of unions.

Around half a million workers from seven different trade unions are set for industrial action on Wednesday, including Holyrood staff who are members of the Public and Commercial Services Union.

Labour failed in an attempt for business to be suspended on Wednesday with items for discussion moved to Tuesday and Thursday – after SNP, Greens and Conservative MSPs rejected the idea.

The Herald understands that Labour MSPs will only cross the picket line if urgent business such as important health matters or discussions around important issues are being debated, and only with the Public and Commercial Services Union giving the party the green light to do so.

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Last week, Labour’s Neil Bibby pleaded with MSPs for business to be moved from the day of strike action.

He said: “In light of that industrial action, we propose to move parliamentary business next Wednesday.

“That business can all easily be done on different days and I am sure that there is a lot that members can work on in their constituencies and regions, including engaging with trade unions.

"That is the course of action being taken by the Welsh Parliament, as proposed by its business committee and agreed by all parties with the exception of the Welsh Conservatives. We should do the same here.”

Mr Bibby added: “There are a number of reasons why it would not be appropriate to go ahead with parliamentary business—not least solidarity with our colleagues—but we should not meet in this Parliament when it is not safe for the public to be in the gallery.

“The idea of us sitting without the people who elected us having the opportunity to join us contradicts fundamental principles on which the Parliament was founded, as does the prospect of committees not hearing from witnesses in person.

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“We believe that the principles of openness and transparency should not be cast aside lightly.

“Public access to the Parliament is essential, and our staff’s role in ensuring public access is essential. Any other course of action would send the message that they are not essential.”

A Labour source told The Herald that Labour MSPs will only cross picket lines for “urgent or serious business” and only “with the agreement” of unions.

As it stands, portfolio questions on the constitution, external affairs and culture as well as on justice are set to take place on Wednesday.

Green MSPs, who voted against Labour’s proposal to move Wednesday’s Holyrood business, will not to take part in Wednesday’s programme, including the party’s two ministers, Patrick Harvie and Lorna Slater.

Greens MSP Maggie Chapman, said: “Scottish Green MSPs will not take part in parliamentary business on Wednesday in solidarity with striking workers.

Read more: Holyrood to close to public during PCS strike

“We are clear that we will not cross any virtual or physical picket lines, and hope that others will join us in that.

“The very rights of the trade union members to strike are under direct attack by the Tory government at Westminster.”

She added: “Everyone who recognises the vital work that Unions have done to support us all should oppose this dangerous and anti-democratic slide towards authoritarianism and stand with striking workers.”

“As parliamentarians, we have a duty to defend those rights. We call on all trade union activists and others to stand tall together against this brutal assault on working people right across the country.”

SNP, Conservative and LibDem MSPs are expected to attend business.

An SNP spokesperson said: "While the SNP recognises and respects the right to strike, the business of government and parliament will continue as normal.”