British Muslims are being urged to go vegetarian next month in a boycott of halal meat.

A boycott is the only way to force the government to take action over "lax" halal standards in slaughterhouses, claimed the community leaders behind the boycott.

Major processors were compromising the Islamic faith by using non-halal methods to produce meat, which was then labelled as halal, according to organiser Abdul Raja.

"I am asking all Muslim customers to make a stand," Raja said. "If we boycott all meat and poultry on Saturdays and Sundays in July, this government will take notice. Money talks."

A diverse range of Muslim clerics and business leaders have tentatively supported the move. It could cost retailers millions of pounds and would be a serious blow to the multiples investing in their halal offers in a bid to win a bigger share of Britain's £500m-per-year halal market.

Naved Syed, director of pie-maker Asli Halal, said it was the only way to ensure standards were tightened.

"It will hit everyone from restaurant owners to kebab manufacturers and retailers," he said. "But it should put real pressure on the government to improve halal standards."

The campaigners' main concern is the use of mechanical slaughtering in halal lines. Animals should be killed by a Muslim with a knife, they said, claiming that many of the major halal suppliers, including 2 Sisters and Sun Valley, were not sticking to this rule.

In a statement from 2 Sisters, it said it was fully accredited as halal by a group of senior Muslim clerics in the EU. But Syed said the accreditation system was not properly audited and called for the introduction for a unified and audited system for the UK.

After a year of lobbying Defra and the MLC, there had still been no progress, he claimed. "Some £5m a year is collected through the levy from halal slaughterhouses. Why isn't any of that put back into the halal sector? We're not even represented as stakeholders."

Sun Valley was unavailable for comment.