(Reuters) - Teachers in Colorado on Monday became the latest in the United States to converge on their state capital to lobby lawmakers for more funding, leading one suburban school district to close for the day.

The move followed strikes in states including West Virginia and Oklahoma that saw thousands of teachers crowd into capitol buildings in successful campaigns for higher spending. Unlike in those states, Colorado’s teachers work under collective bargaining agreements that prohibit strikes.

The Colorado Education Association said it expects more than 500 of the 35,000 teachers and support workers it represents to come to the Colorado General Assembly in Denver to urge legislators to increase education funding and strengthen their retirement plan.

“We have many educators who are working two and three jobs, renting out rooms in their homes to make ends meet,” union president Kerrie Dallman said by phone.

Teachers in Kentucky and Arizona have also joined in recent campaigns to demand increased education funding and teacher pay.

Colorado’s union asked teachers either to take personal days and come to the capitol or to hold informational meetings with parents before the start of the school day in their districts.

Any increase in education funding would need to come from other programs, since the state cannot increase taxes without a public referendum.

At least one district, the Denver suburb of Englewood, said it would close its public schools for the day because of the teachers’ action.

The National Education Association ranked Colorado 46th in average teacher pay in 2016.

Low teacher salaries, which start at around $29,000 a year in some rural areas, have left Colorado with 3,000 teacher vacancies, Dallman said, citing a state report. They are being filled by increasing class size or with long-term substitutes who may not be well versed in the subject matter, she added.

The union also aims to improve a state pension plan that a Senate bill would weaken, Dallman said.

Republicans, who control the state Senate, said they needed to shore up the public employee pension plan because unfunded liabilities had ballooned to $32 billion in 2016 from less than $1 billion 20 years earlier.

The bill would increase employee contributions, raise the retirement age, cut cost of living increases for retirees and add a defined contribution option which would give participants a lump sum payout, instead of lifetime payments, at retirement.