Many of the rooms at the National Gallery were closed last week. More than 200 staff were on their second five-day strike over plans to outsource security and visitor services. In the rooms that were open, the remaining attendants were hovering awkwardly near their chairs. CIS, the private contractor brought in to staff the recent Rembrandt exhibition, bans its employees from sitting down. I asked one of them how he felt about the arrangement. ‘I honestly don’t know why they’ve put chairs here,' he said. 'But I like walking around, it means I can speak to people. If I was sat down nobody would speak to me.’

When CIS was drafted in last autumn, a gallery spokeswoman told me the exceptional circumstances of the show demanded a new approach: ‘Obviously Rembrandt is a major international exhibition and we wish to be able to ensure maximum access to the public.’ But they showed no signs of leaving when the show closed last month. The staff union, PCS, was concerned the company had been brought in to break resistance to the outsourcing plans. The union also fears that CIS is being lined up to step in when the full contract goes out to tender in May. One rep – speaking anonymously after the gallery threatened disciplinary action against staff members who speak out – said there was now a large surplus of gallery staff on shift at any given time.

This approach from management – which says it has been forced to ‘appoint an external partner’ because of PCS’s opposition to a new roster system – has done little to convince workers they can make progress through ongoing negotiations. One employee told me she had seen an HR manager taking photographs of pickets one morning; the gallery strongly denies this. And on the eve of January’s walk-out, a senior union rep, Candy Udwin, was suspended for allegedly disclosing a confidential figure about the cost of outsourcing to union staffers. Udwin turned up with her colleagues to a conciliation session last Tuesday, but gallery managers didn't let her take her seat at the table.

On Thursday pickets and supporters marched to Getty Images Gallery, off Oxford Street, with a letter urging Mark Getty, the chairman of the National Gallery's board of trustees, to consider their proposals for reforming the gallery. Shift patterns can be changed and opening hours extended without resorting to privatisation, they say.

Visitors I spoke to were sympathetic. ‘I personally support the strike action very much,’ said Pino Cimino, who has been visiting the gallery since he was an art student in the 1970s. ‘The staff here are almost friends. They know everything about the gallery, even if they see a little speckle of dust they know why it’s there. If you put agency people in here, they won’t be emotionally involved with the paintings.’ Another visitor, on her way to the tea room, was more ambivalent. ‘If it’s the right specification, then they’ll get the right people,’ she said. ‘But if they end up with people who don’t know about the paintings then I’d support this protest.’ Management insists employees will be transferred to the new contractor, and their conditions protected. Reps say you only need look to the Sainsbury Wing; when I asked a CIS guard there for information, she replied: ‘Sorry, we’re just security.’