Lawmakers are looking to impose mandatory standards to protect chemical plants from terror attacks after a Bush administration report showed that federal legislation is needed to close the gap left by voluntary compliance.

Sen. Susan Collins (search), R-Maine, chairwoman of the Senate Homeland Security and Governmental Affairs Committee, has said that she would like to have a bill drafted by the end of the summer and approved by the Senate before the end of the year.

The Environmental Protection Agency has identified 123 chemical plants in the country that are high risk, meaning that if they were hit by terrorists, upwards of 1 million people would be affected.

Collins said during a Wednesday hearing on the hill that the plants are "ticking time bombs."

"These chemical facilities are not hidden. We know they exist, we know precisely where they are and what they contain, and so do the terrorists," she said.

According to witnesses at the hearing, voluntary security standards are not followed by everyone. In fact, 20 percent of the high risk plants, all located near large urban centers, do not follow the voluntary code.

Robert Stephan, acting undersecretary for information analysis and infrastructure protection at the Department of Homeland Security, testified that the present system has created essentially a big black hole, and both the federal and state government cannot say with any certainty that the plants are adequately secured. However, Stephan warned that coming up with regulations available for public comment as well as other scrutiny also begs the question of whether that would improve security.

"If we put a detailed regulation out that says every chemical facility will approach it in this manner using the following steps, I don't know a better cookbook to give to Al Qeada (search) that outlines exactly the level of security by facilities across the country," he said.

While the industry has in large part opposed mandates, some chemical plant executives favor legislation to level the playing field, saying that while some companies have invested heavily in security others have not laid out much at all.

FOX News' Catherine Herridge contributed to this report.