The Minnesota DFL plans to launch a major ad campaign starting next week to support Gov. Mark Dayton's re-election bid.

Ken Martin, state party chair, said Wednesday the party will spend more than $1 million on the ad barrage. He would not say what message the ads will contain.

"It's a very significant buy," Martin said. "We haven't seen anything from the other side yet in a real way."

The DFL's $1 million ad buy is one of the biggest the low-key governor's race has seen. There is little public evidence that the state Republican Party, still paying off old debts, has plans for paid television ads.

Dayton and Republican challenger Jeff Johnson have not yet aired any television ads, although the DFL governor has some ad reservations lined up for later in September.

The anti-Dayton Freedom Club spent six figures on ads before the primary but went silent for a few weeks. Public documents indicate Freedom Club is ramping up for second ad campaign. The pro-Dayton Alliance for a Better Minnesota has also spent on ads.

Both of the two main contenders for the governor's post are furiously raising cash. According to reports filed this summer, Dayton had raised more than three times what Johnson had and had more than six times the cash banked than had his Republican rival.

Johnson faced a competitive primary in August and has been spending significant time raising money since his win.

On Tuesday, Martin said Johnson was being disingenuous about his connection to the Tea Party.

"This is a question of character," said Martin, who accused Johnson of trying to "reinvent" himself post-primary.

"It's the hypocrisy. It's the lying. It's the misleading," Martin said.

To bolster his case, Martin shared a video of Johnson at a Tuesday news conference saying he had not sought the Tea Party's endorsement and questioning whether the Tea Party even endorses.

The DFL compared that to a video of Johnson at a South Metro Tea Party meeting in April, where he is shown telling the crowd: "I would be truly honored to earn your support and endorsement in this race."

Johnson campaign spokesman Jeff Bakken said Johnson was asking for the support of individual Tea Party members in advance of the Republican Party state convention, where most of them would be attending. Johnson has frequently spoken at Tea Party gatherings across the state and been welcomed by Minnesota Tea Party leaders and meeting attendees.

Bakken said he expects the DFL's accusations to have little effect.

"Minnesotans are smarter than the Democrats think they are and will see these silly, juvenile attacks for what they are: meaningless tripe being peddled by people and politicians terrified of losing their power," he said.

The Johnson campaign will hold a news conference on Thursday that Bakken said would "highlight a fundamental difference between Mark Dayton and Jeff Johnson."

Rachel E. Stassen-Berger Twitter: @rachelsb