Mason, in a case seen as emblematic of voter suppression, faces over five years in prison for a mistaken vote that was not counted

Crystal Mason, the woman who became the poster child for voter suppression when she was sentenced to five years for casting a ballot in Texas, has gone into federal prison at the start of her ordeal.

Mason, 43, surrendered voluntarily on Thursday to authorities and was taken into federal prison in Fort Worth, Texas. She left her three children behind.

In her final Facebook post before she went inside, she wrote: “This fight is not over, I’m glad God choose me for this journey. I’m walking in there no tears and head hung high …”

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Mason’s crime was to cast a ballot in the 2016 presidential election. An African American woman, she had been encouraged by her mother to do her civic duty and vote, in her case on behalf of Hillary Clinton.

When she turned up to the polling station her name was not on the register, so she cast a provisional ballot that was never counted. She did not read the small print of the form that said that anyone who has been convicted of a felony – as she had, having previously been convicted of tax fraud – was prohibited from voting under Texas law.

The Guardian highlighted her plight last month.

US voter suppression: why this Texas woman is facing five years' prison Read more

For casting a vote that was not counted, she will now serve 10 months in the federal system. While locked up it is likely that her final appeals in state court will be exhausted, which means she could be passed at the end of the 10 months directly to state custody for a further five years.

Her lawyer, Alison Grinter, said she was dismayed to see Mason ripped from her family. “This is an act of voter intimidation, not the will of a free people.”

Grinter added: “Make no mistake: this is a clarion call to our over-policed and over-prosecuted communities of color. You are not welcome in the voting booth, and any step out of line will be punished to the fullest extent of the law.”

Mason’s case is one of the more dramatic examples of voter suppression in Texas. The state has been at the forefront of Republican moves to place hurdles in the way of voting since 2013 when the US supreme court overturned a key element of the Voting Right Acts that had prevented largely southern states from discriminating against minority citizens.

The state has one of the most strict voter ID laws in the country, requiring individuals to show proof of identity, and to register to vote at least 30 days before any election. Fort Worth, under its Republican district attorney, has been particularly hardline, not only prosecuting Mason but also going after a Hispanic woman, Rosa Ortega, for mistakenly voting as a non-US citizen.

Ortega, 37, who had permanent resident status in the US having come to the country as an infant, was sentenced to eight years in prison to be followed by deportation to her native Mexico. Since her conviction she has disappeared and is presumed to have self-deported.

Fort Worth’s harsh treatment of illegal voters is paradoxical in that it has among the worst turnout rates in America. In recent city council elections, the turnout was 6%.