Western Australia's Prison Officers' Union says a record number of inmates in the state's prison system shows the Government is not committed to the safe operation of WA jails.

More than 5,600 people were behind bars as of Friday afternoon, in a system the union said was designed to hold just 4,000.

It claimed a number of facilities including the state's main maximum-security jail, Casuarina, were struggling to cope with the load.

Union president John Welch said Casuarina was short-staffed by about 30 people on Friday, despite calling in all available extra officers.

The prison generally operates with a staff of about 100 people.

Mr Welch said services had to be dramatically cut back and extra lock-downs were enforced as a result.

"The Government has been locking more and more people away, but has been too slow to build new prison cells to accommodate them," he said.

"On top of that, we have a shortage of staff, which we have been warning the minister about for more than a year, yet he didn't react swiftly enough to recruit more officers.

"If you decide you're going to lock more people up then you need to have more facilities in which to house those people.

"If you decide you're going to have a policy which increases the prison population you need to make sure you actually have capacity to manage it safely."

Minister 'too slow' to address overcrowding: union

The claims are the latest in a verbal stoush between the union and the Government, which is set to introduce new laws targeting corruption among prison workers.

Late last week Corrective Services Minister Joe Francis said the new laws would save taxpayers up to $1 million a year, a suggestion which was rubbished by Mr Welch.

He has accused the minister of being too slow to address overcrowding.

"Maybe if Joe Francis spent more time concentrating on what was actually going on in his portfolio than going on some witch hunt after prison officers, then the prison system wouldn't be having the problems that it's currently having," he said.

In a statement Mr Francis described the union's concerns as nonsense and "typical of a Labor Party affiliated union."

"[It has] no interest in stamping out corruption amongst its members," he said.

"No honest, hard-working prison officer has anything to fear from the new discipline regulations."

Mr Francis said the state's prison system was not overcrowded and there were 1,200 spare beds, with capacity set to increase when construction of the new Eastern Goldfields Regional Prison was completed in the coming months.

"It wouldn't matter if there were half the number of prisoners and twice as many prison officers, the union would still claim the prisons were overcrowded," he said.

"I am not in the business of employing prison officers to guard empty cells."

Mr Welch said the minister's assertion of 1,200 spare beds came from a Government decision to change how it classed cell capacity, and was not a true reflection of capacity.

He said the current overcrowding problem was likely to be exacerbated as summer progresses.

"In the hot heat of Perth's summer it becomes very difficult when you're trying to shoehorn two people into a cell designed for one," he said.

"We need to ensure that prisoners are housed in appropriate circumstances so that we can provide programs and education we need to reduce recidivism and lead to a safer and better WA."