He said they were "killing my business".
Mr Kumar said he called the police "every day" about the issue.
National MP Jami-Lee Ross' bill is aimed at the window washers at intersections and
bans people washing a car or a part of a car on a road if it is unsafe, causes an
obstruction or "may intimidate or cause a nuisance" to others.
If the bill is passed, window washers at intersections could be fined $150 on the spot by the police. The Transport and Industrial Relations Committee is currently considering the bill.
Rotorua already has a bylaw to stop window washers - but it has to prosecute people
to enforce it, with a maximum fine of $20,000.
Mr Kumar said he was worried if the bill was only for intersections it would be "back to square one".
"It doesn't solve the problem, they'll basically move to the shopping centre."
But Mr Kumar was also concerned about the window washers.
"They need support. Why are they doing this? There is no support for them. Where can they go for help if they are having financial difficulties?"
Local window washer Brian 'BamBam' Mollgaard said he had been doing it for 25 years "on and off", using a mixture of dishwashing liquid and methylated spirits to clean the windows.
He wasn't impressed about the possible fine.
"If they just leave us alone, we're just making a couple of bucks."
Mr Mollgaard sees what he, and others like him, do as helpful.
"It's getting rid of the pollen and grime off people's cars."
He said he only washes a car's window if the people inside said yes when asked, out of courtesy and respect.
The money he made from window washing he spends on necessities such as bread, milk and sugar, and it's not his only job - he also mows lawns and chops wood.
He said he did understand some people's opposition to window washers.
"[Window washers] scare them."
Rotorua police area prevention manager Inspector Stuart Nightingale said he had received complaints about some window washers being disruptive and sometimes intimidating.
Mr Nightingale said at times police have had to intervene and take action.
"I'm not aware of any road rage but I am aware of upset shop owners and some intimidation leading to complaints... I completely understand their position, they have a business to run and [window washers] shouldn't put people off."
He said he thought the bill would make the current prosecutorial side easier.
And Mr Nightingale was understanding of the window washers' situations.
"I would like to think the frontline police would apply common sense and human factor and consider why people are doing this. For some their income is created by doing [this] service but the public perception is linked to being a nuisance and intimidation."
The public are able to put in submissions on the bill until June 1.
