The move has infuriated some members of the tight-knit St Elizabeth's School community, who have accused the Dandenong North school of political interference and intimidation.

It also prompted federal Education Minister Simon Birmingham to phone the school on Friday to inform it that it would receive an additional $5.9 million of federal funding over the next decade.

On Thursday, students at St Elizabeth's were sent home with letters that said the federal government's Gonski 2.0 plan could lead to higher fees at Catholic schools and cuts to programs.

Parents were asked to sign the letters and return them to the school - then they would be sent to Bruce MP Julian Hill in batches.

"I am very concerned about the future funding arrangements at our school," the letter read.

"I need to start thinking about what I will need to do to educate my child next year."

A notice to home group teachers, obtained by Fairfax Media, asked them to explain to students that "they have to get a parent to sign the letter".

"When you give the letters to the children explain to them that every class that brings back every letter signed gets to wear casual clothes on Friday June 2," it read.

This same message was also conveyed in the school newsletter, which read : "This week a letter came home for you to sign and return to school ... the children will probably pester you to sign the letter so that their class can have a casual clothes day on June 2."

A parent said principal Christine Ash told students over the school loudspeaker that if they did not bring back the signed letters, the entire class would miss out on a casual clothes day.

"God help the one kid who costs the rest of the class a casual clothes day," they said.

"The whole class would be punished. It was a way of bullying the class to sign the letter. It was completely inappropriate."

But a Catholic Education Melbourne spokesman said parents were asked to return the letter regardless of whether it was signed, to show that it had been read.

He said there was no onus to sign, and it was not tied to participating in the casual clothes day.

He did not say why the school told parents and students otherwise.

He said electronic communication was sent to parents on Friday which read "the letter we sent out yesterday which we can send on your behalf to our federal member of parliament can be returned to school signed or unsigned".

Mr Birmingham said the reforms would ensure all schools were treated fairly.

"I think all reasonable Australians would expect school administrators to be focussed on improving our declining literacy and numeracy results and not using parents and students as pawns in a political scare campaign," Mr Birmingham said.

"Our plan invests $18.6 billion to fund a record share of government school costs regardless of state borders but based on the individual need of each school and ensures that taxpayer support for non-government schools is also based on need, regardless of system or faith."

The minister said that the growth in federal funding to the Catholic Education Commission of Victoria meant there should be no reason for school administrators to hike fees.

The commission has launched a grass-roots campaign against the changes, and is coaching principals on how to raise concerns with their local MPs.