FORT WORTH, Texas (AP) — An environmental group is attempting to force the U.S. Environmental Protection Agency to tighten Texas air pollution control permits that it says have loopholes that allow for illegal emissions, according to five federal lawsuits filed against the agency Thursday.

The suits brought by a coalition led by the Washington, D.C.-based Environmental Integrity Project target Texas-issued permits for the ExxonMobil Baytown Olefins plant and refinery, the largest integrated petrochemical factory in the U.S.; Petrobras' Pasadena refinery; the Saudi-owned Motiva Port Arthur refinery, the largest petroleum refinery in the U.S.; and SWEPCO's Welsh coal-fired power plant east of Dallas.

For years, the group claims, power plant and refinery operations have polluted almost without penalty because of a loophole in Texas permits that allows for excessive emissions when machinery malfunctions or undergoes maintenance.

"EPA knows that Texas issues unenforceable permits with illegal loopholes that render useless some of the most basic pollution control requirements of federal and state law," Gabriel Clark-Leach, one of the group's attorneys, said in a statement.

As a result, Texas' environmental regulatory agency imposed financial penalties in less than 3 percent of nearly 25,000 illegal air pollution incidents from 2011 to 2016, according to the nonprofit's analysis of state records released earlier this month. The fines totaled $13.5 million.

The report concluded that the paucity of state fines, averaging about 3 cents per pound of pollution, meant that owners of aging facilities were less likely to invest in upgrades and repair known problems.

The Texas Commission on Environmental Quality called the analysis "misleading."

Spokesman Brian McGovern said the agency does not allow industries to emit excess amounts of air pollution during breakdowns or maintenance.

"TCEQ rules require that emissions be minimized and equipment be properly maintained, along with several other factors, and compliance with these requirements is considered before initiating enforcement," he told The Associated Press.

He added that the state's enforcement rate was actually 7 percent of nearly 27,000 illegal emission events during the period, although that number includes cases in which the agency issued notices of violation without imposing financial penalties.

"That's a disturbing admission," the nonprofit's spokesman, Tom Pelton, said, "because this means the state admits it allows 93 percent of these illegal pollution incidents go without even a violation notice."

The Clean Air Act says that the public can petition EPA to object to state-issued emission permits when the permits appear to undercut federal standards. EPA has objected to three Texas-issued permits since 2015 after the Environmental Integrity Project sued the agency for failing to respond to public petitions, the group said.

Thursday's lawsuits come about in light of a recent decision in a federal case brought by Houston-area residents and environmental advocacy groups in 2010. In April, U.S. District Judge David Hittner imposed a $20 million fine on ExxonMobil for emitting 10 million pounds of air pollutants from its Baytown complex during malfunctions and maintenance during an 8-year period.

In his 101-page ruling, Hittner also agreed with environmental groups that ExxonMobil had saved some $14.2 million by not complying with clean air act rules and regulations.