SALEM, Ore. — A day after the Republicans refused to be at the Capitol in protest of a cap-and-trade bill, the Oregon Senate convened Friday with only Democrats present.

After calling the session to order at 9 a.m., Senate President Peter Courtney abruptly ended the session. On the hour each hour Friday, the session was announced as remaining in recess.

Oregon Gov. Kate Brown has authorized Oregon State Police, a division of her executive branch, to round up the missing senators and bring them to Salem to create the necessary quorum to enact legislation.

RELATED: Gov. Brown sends police to find walkout GOP senators: ‘They need to return and do the jobs they were elected to do’

MORE: What's next with walkout?

Democrats in Oregon control both the House and the Senate. Democrats have an 18 to 12 majority in the chamber, but need 20 members present for a quorum. One GOP senator recently died and has not yet been replaced.

Republican Sen. Tim Knopp, who represents Bend, told KGW he is out of the state but alone. He said the senators remain united and in contact about the walkout.

"We had about 1,000 loggers in the Capitol the other day and it didn't seem to have any impact on the thinking of people who are pushing this bill forward," Knopp said over the phone. "So, the only options we had to slow this bill down and get the attention of the public and the majority was to deny a quorum and walk out."

Watch interview with Sen. Knopp

OSP was mum Friday morning on the details of bringing back senators.

In a prepared statement, OSP said the governor's directive has not affected responses to emergency calls. No senators have been brought back to Salem by troopers, it said.

RELATED: Q&A: How will Oregon State Police go about finding GOP senators who walked out?

Several senators have been in contact with OSP but the agency declined to comment further. They also declined to answer questions on the costs of the roundup or if other police department were assisting in the search.

When Brown threatened to use police to bring back Republicans, a GOP senator from Dallas threatened violence against OSP.

MORE: ‘Send bachelors and come heavily armed’: GOP state senator responds to Gov. Brown’s police threat

Another session was planned for Saturday but that session was canceled following reports of a planned rally "that may include militia group members," KGW's Pat Dooris reports.

RELATED: Oregon Senate session on Saturday canceled due to safety concerns over planned rally

Cap-and-trade bill

Under the proposed cap-and-trade bill, Oregon would put an overall limit on greenhouse gas emissions and auction off pollution "allowances" for each ton of carbon industries plan to emit. The legislation would lower that cap over time to encourage businesses to move away from fossil fuels: The state would reduce emissions to 45% below 1990 levels by 2035, and 80% below 1990 levels by 2050.

Read HB 2020, the cap-and-trade bill 

Democrats say the measure is an efficient way to lower emissions while investing in low-income and rural communities' ability to adapt to climate change. It has the support of environmental groups, farmworkers and some trade unions.

Those opposed to the cap-and-trade plan say it would exacerbate a growing divide between the liberal, urban parts of the state and the rural areas, which tend to be more conservative. The plan would increase the cost of fuel, damaging small business, truckers and the logging industry, which is already in freefall due to federal environmental protections, they say.

Watch: What is cap and trade?