A union has paid for a huge billboard expressing 'no confidence' in the embattled Broward County Sheriff months after he was heavily criticized over the Parkland massacre.

The yellow sign on Interstate 95 just north of Sunset Boulevard tells Florida Governor Rick Scott 'there is no confidence in Sheriff Israel'.

It was funded by the Broward Sheriff's Office Deputies Association, which in April passed a vote of no confidence in the Democrat supported by 534 of the 628 of voting members.

The yellow billboard on Interstate 95 just north of Sunset Boulevard tells Florida Governor Rick Scott 'there is no confidence in Sheriff Israel'

The Association wants Governor Scott to suspend or fire Israel. However Scott, a candidate for the US Senate, said he is waiting for the outcome of an investigation into the sheriff's handling of Parkland, the Sun Sentinel reported.

The sheriff's office failed to act on 18 warning calls about shooter Nikolas Cruz before he killed 17 people at Marjory Stoneman Douglas High School on February 14.

The tips were among a series of what authorities now describe as the clearest missed signals that Cruz, who had a history of disturbing behavior, posed a serious threat.

Explaining the billboard, which will be up for a month and is set to be seen by 500,000 passing motorists, union president Jeff Bell said: 'We are going to continue to speak out loud and make sure our voice is heard.

'It's a strong message to put it right in front of Rick Scott of how serious we are.'

Israel blamed school resource officer Deputy Scot Peterson for staying outside the school building while opened fire with a Cruz AR-15 semi-automatic rifle. Peterson was suspended without pay and chose to retire.

The Broward Sheriff's Office Deputies Association wants Israel (left, on February 21) to be dismissed by Governor Scott (right, on May 4)

Bell said Israel should not have publicly singled the deputy and should have placed him on paid leave until an investigation into his conduct was completed.

He said only deputies accused of crimes are placed on unpaid leave and Peterson has never been charged.

Israel also angered critics after the shooting by boasting about his 'amazing' leadership in a televised interview.

The sheriff issued a statement on Friday saying it is 'unfortunate and appalling' that Bell is using the school shooting 'as a bargaining tactic to extort a 6.5 percent pay raise' for the union's members.

Explaining the billboard, union president Jeff Bell said: 'It's a strong message to put it right in front of Rick Scott of how serious we are'

The 3-year-old union represents the office's deputies who hold the rank of sergeant and below, and its contract expires September 30.

Israel was overwhelmingly re-elected to a second term in 2016. Republican Governor Scott rejected calls from some state legislators to suspend him after the shooting.

Cruz's lawyers have conceded he is the shooter and say he will plead guilty in exchange for a life sentence. Prosecutors say they will seek the death penalty.